The Boat:
She is a 2007 36 footer, and was purchased by her current owner in June of 2015 in Nova Scotia, and then sailed back to Maine. At commissioning in Nova Scotia the batteries were found to be "dead". The broker ordered and had installed two brand new Costco/Kirkland "Deep Cycle" Group 27 batteries rated at 115Ah each..
One of the murdered batteries during autopsy.
NOTE: Beware this identical battery may also be wearing an Interstate branded sticker at some Costco stores.
EDIT: As shown above I recently cut open one of these batteries and found they were not at all deep cycle but rather a very thin plate dual purpose bordering on starting batteries that had a "deep cycle" sticker applied to them. Buyer beware!
I was supposed to be on the delivery trip but could not make it due to a last minute schedule change having to do with the boat not actually being ready. I walked the owner through all the things that should be checked and that could go wrong and I loaned him numerous tools for the trip. They set off across the gulf of Maine in little to no wind but they did have brand new batteries.
Deep Cycle Stickers on El-Cheapo Batteries = RIP OFF
When buying batteries please try & stick with a brand name, unless you know EXACTLY what the product really is under the re-labelers sticker. Trojan, Rolls, Deka/East Penn, US Battery, Dyno, Crown, Lifeline, Full River, Firefly, Odyssey, Northstar etc. are all reputable brands that offer deep-cycle products in their line-ups..
Sticker brands such as Kirkland, Power Star, All Rounder, Energy Master, Auto Craft, Powertron, Super Start, Maxx Marine, Cabella's, Duralast, Sportsman etc. etc. are all STICKER-BRANDS and you have little to no idea what you are really getting unless you do some extensive leg work.
I can say without a doubt, because I physically cut them open & measured the plate thickness, these batteries were not "deep cycle" and probably not even a true "dual purpose" battery, they were low budget automotive grade batteries wearing a "Deep-Cycle" sticker.
When companies slap a sticker on a battery mistakes get made and misleading marketing can rear its ugly head. Rather than go into what to look for in a deep cycle battery here, click below for more info:
What is a Deep Cycle Battery? (LINK)
Heat Murders Batteries:
When the boat got to Casco Bay I immediately went to work on her. The factory layout was horrible with both of the "new" batteries in the engine compartment. Heat murders batteries, and while this does not happen instantly heat and low SOC are not good for longevity. These batteries had already likely exceeded 125F on a few occasions. I actually measured the case temp of one of them at 117F when they came into the anchorage after a multi-hour motor in no wind. They also had to motor for approx 13 hours of the delivery trip due to zero wind. It was clear the upgrades would start with getting the batteries out of the engine space.
Seeing as budget was short but cruising plans were on the calendar, I set out to relocate the two new batteries & get them out of the engine bay. I also planned to wire the two new batteries as a hard-wired parallel house bank. I had a used but otherwise good condition group 31 battery that I gave to the owner as a "starting battery" and we left it in the engine bay for this season. In the image below there had been two group 27's and now there is just one group 31 acting as a starting battery. Still, this is a a very poor location for batteries.
Partial State of Charge (PSOC) Cyclic Use Murders Batteries:
The alternator can also be seen in the image below, as well as a number of safety flubs that needed correction, and is a bone stock Paris-Rhone automotive alternator. A shortcoming of this alternator is that it temp-compensates and reduces the absorption charging voltage as the alternator heats up. This type of temp protection for the alternator, is not at all healthy for deeply cycled batteries.
Because of the way this alternator self protects itself it leads to chronic under charging and an absorption voltage that is far to low and incredibly unhealthily for the batteries. On the list for this boat, to correct this short coming, is external regulation.
Because of the short engine run times on sail boats, and the insanely low voltages we were measuring at the batteries, these batteries were suffering from pretty harsh PSOC use.
PSOC cycling use means that we never fully recharge the bank before discharging the bank again. When we PSOC cycle lead acid batteries they suffer two things. The first is a phenomenon called "capacity walk down" which begins as early as cycle #1. The walking down in capacity is caused by the number two item, which is sulfation. Essentiaally PSOC walk-down and sulfation means or necessitates that each day you actually need to run your engine a bit longer and longer to achieve the same usable capacity. So if you charged for 1 hour per day, at a steady 40A, and assumed you were getting 40Ah back in think again. The usable capacity will continue to walk down a bit with each PSOC cycle. The only way to slow the effects of PSOC cyclic use is with frequent full charges and equalizing the batteries regularly. For more info on PSOC cyclic use, and its effects, see the May 2015 article in Practical Sailor -
Fighting Sulfation In AGM's
Incorrect and Inaccurate Voltage Readings Can Murder Batteries:
The boats analog DC volt meter was horribly inaccurate and was not working correctly. The owner checked battery voltage using the volt meter but had no idea it that was inaccurate. On battery #1 the analog volt meter was reading +0.9V off , on the high side, and for bank #2 +0.8V high. This does the batteries no favors because at 12.1V the batteries were respectively at 11.2V and 11.3V which is essentially DEAD. Discharging the batteries to this level will rather drastically shorten their usable cycle life, especially starting type batteries masquerading as "deep cycle"...
Let's Just Try and Get You Through The Season:
The two new Costco batteries were moved to a cooler location below the starboard quarter-berth, where they should have been all along, the builder even had a shelf for them already built into the hull liner.. Unfortunately the platform molded into the hull liner prohibits flooded batteries being mounted in the proper orientation so the owners next bank will be AGM.. The Costco batteries were charged and equalized briefly during this conversion. The battery cabling was all well sized by the builder, at 2/0, so new jumpers were made of 2/0. The batteries were secured and wired in parallel for a house bank. At the same time an ACR was added to charge the starting battery. Some other wiring changes were also made to make it easier for the owner to operate.
Better SOC Monitoring:
The owner was not up to installing solar this year and the boat resides on a mooring, not having solar on a mooring is a terrible situation for batteries on a sailboat..
I explained to him that I was doubtful his Costco batteries would make it into season two, but he suggested season two would have more budget for things such as solar & newer and higher quality deep cycle batteries. The choice was made to install a Smartgauge this year so he could better track SOC and help try to keep his bank healthy enough to get through the season. The Smartgauge was already part of his long term plan so installing it for this season, considering the inaccuracy of the on-board volt meter, seemed like the best fit.
Time to Decommission:
When I went to decommission the boat the owner had been running the water pump to drain the tanks. We stopped and let the Smartgauge sit for about 1 hour and it stabilized at 38% but with the LED lights on, and the stereo, the SOC kept dropping until I disconnected the bank at 34%. The owner was lamenting that the SOC had been dropping more rapidly as the summer grew on but that he had "learned" how long he could run loads, not very long..
In total he and his family did approx 25 over-nights that resulted in deep-cycling the batteries to approx 50% SOC. There were also a fair number of very deep discharges, perhaps 8-10, before the Smartgauge was installed. There were also 5-6 days of racing with the fridge running and in these scenarios they usually sailed on and off the mooring with no charging.
After the Smartgauge was installed the owner tried very hard not to let it drop below 50% SOC but as the batteries grew tired, keeping them above 50% SOC became a losing proposition. Even with a ten hour motor one weekend, from Portland, ME to Isle Au Huat, ME, with zero wind, the batteries still never reached 100% SOC, due to sulfation.
The SOC in the fall when the batteries were removed:
Testing The Bank:
This scenario created a good opportunity for me to not only test the accuracy of the Smartgauge but to also test the batteries for their current state of health.
I photographed the Smartgauge at 34% SOC then removed the batteries and took them back to the shop for testing. The batteries were wired in parallel, just as they were on the vessel, and connected to one of the Ah capacity testers. Look close and you can clearly see the 5/15 date code stickers on the batteries. Brand new as of May 2015...
I did not recharge the batteries before discharging them to the industry standard of 10.5V under their rated 20 hour load. The batteries delivered a paltry 20.22Ah's before hitting 10.5V!! This is a 230Ah rated bank so at 34% SOC it should have delivered somewhere in the neighborhood of 78Ah +/- before hitting 10.5V. I knew the batteries were in bad shape when they could barely muster 20Ah's from a reported 34% SOC..
I then fully charged the batteries and floated them for two full days beyond the absorption charging and ran a full capacity test at the 20 hour "as new" rate. The battery case temps hit a low of 74F and a high of 78F, well within reasonable for this testing. This time they delivered a measly 52.94Ah. You read that correctly, they were delivering just 23% of their factory rated capacity in just 4.5 months. A dead battery, by industry standards, is anything less than 80% of its as new factory Ah rating!! 23% is really quite murdered...
The good news is that 52.94Ah, in total capacity, compared against 20.22Ah, from the 34% Smartgauge measurement point, we were within 4% accuracy of the batteries actual physical capacity. This 4%, for a battery that has been pretty murdered, is an exceptional feat for the Smartgauge. I know of no other battery monitor in existence that could have predicted this massive decline off the abyss as accurately as the Smartgauge did.
If this had been a traditional Ah counter the bank capacity would still have been programmed for 230Ah's with an actual capacity of just 53Ah's... Think about that for a moment...
Never satisfied with "good enough" I decided to do a full equalization of 8 hours at 15.5V. The batteries were charged until current declined to well under 1A at 14.6V then the voltage was brought up to 15.5V and held there for 8 hours. I then re-tested the batteries for capacity at the 20 hour as new rate. This time they delivered 56.41Ah, an improvement of 3.47Ah. I repeated the test a second time with an additional 2 hours of equalization and netted within .4Ah. This was the most we were ever going to see out of these murdered batteries.
I also split the batteries and ran individual capacity tests. I wanted to see if one battery was the culprit or was it both of them more equally? Battery #1 tested at 28.04Ah and battery #2 tested at 28.32Ah. Both batteries were within 0.28Ah of each other, so they died pretty evenly, but they still died a pretty quick death.
This test ensured we did not have one really bad battery and one marginally good one propping the other up.
The good news? The equalization process brought the Smartgauges 34% SOC reading, and accuracy, down into the 2% range, in the real world and in an abusive environment. This is really quite remarkable.
Specific Gravity is not a good tool to determine State of Health or Ah Capacity:
To many I know this will sound like blasphemy, but save your clothes from acid burns...... How on Earth can I say that? Well for starters each of the 12 cells measured as near identical as you can get. The batteries were not out of balance in any abnormal manner. They also hit a specific gravity of 1.280 when fully charged. Yes they were "fully charged" but instead of 230Ah's they could only deliver 53-56 Ah's. Specific Gravity can tell you SOC, like the Smartgauge, but not SOH / state of health. A good specific gravity reading tells you nothing about the batteries actual capacity just its SOC, which the Smartgauge can do externally with no acid burns..
Here we have a bank delivering at best 24.5% of its advertised capacity (230Ah rated delivering 56.41Ah after EQ) in somewhere around 35-40 cycles most likely due to sulfation, being the wrong battery type for the application, a dumb alternator regulator, never getting fully recharged after each use and possibly some effects from heat.. Yes these batteries also had a few super deep cycles but any deep cycle battery should handle the occasional dip to 20% SOC with ease, if otherwise properly charged and properly selected for deep cycle use..
Lessons Learned:
*All lead acid batteries need to get back to 100% SOC as often as possible. A stock alternator on a mooring sailed boat is simply inadequate for optimal cycle life. For mooring sailed boats and battery longevity a small solar array can do wonders.
*Cheap Group 24, 27 & 31 flooded batteries are not deep-cycle just because the sticker says so. I have a good hunch these are actually starting batteries not even dual purpose, but they wear a "deep cycle" sticker.
*Due to the liner pan and clearance, the batteries were mounted in an improper orientation for the cells/plates on a sail boat. The vessel design precludes proper orientation of a sufficiently sized flooded house bank without doing some serious $$$ modification.
*The label on these batteries is likely a complete and utter hip shoot. I find it hard to believe that these batteries could have ever delivered 115Ah even when just barely broken in. They faded so fast in Ah capacity that I've only seen this once before, and they were starting batteries that had been mislabeled by a regional distributor.
*These batteries weigh considerably less than a Trojan group 27 so they are likely closer to a starting battery than a dual purpose.
*Unless you are getting 14.4V(bare min for flooded batteries), at the battery end of the charging circuit, but preferably 14.6V to 14.8V, you will wind up chronically under charging and will kill your batteries earlier due to sulfation. The absorption stage of charging is the healthy part where the lead sulfate is reconverted. If you never attain an absorption voltage, due to voltage drop and an unsuitable alternator design for a cycling bank, then the batteries will die sooner than later. In this case murdered in one short 4 month season.
*Sulfation murders batteries quickly, if you allow it to. Batteries need to get back to 100% SOC as soon after a discharge as possible. This simply does not happen on most sailboats with alternator only charging.
*Heat kills batteries. While the effects of heat are not instantly murdering batteries lead sulfate hardens and becomes un-reconvertable faster in warmer temps than it does when batteries are kept cooler. Deep cycling and heat do not play well together.
*If you are on a mooring solar or wind charging is going to be pretty critical.
*If you want to know your SOC the Smartgauge actually works and is very simple for the average boater to understand.
*Inaccurate voltage readings can actually lead to a worsening of the battery condition. Analog volt meters can be horribly inaccurate in the marine environment so please compare these readings to a meter with known good accuracy.
*Specific gravity readings tell you nothing about state of health or Ah capacity only SOC. The specific gravity readings on these batteries showed them in good balance and showed them attaining a full charge yet that full charge lacked any real stored capacity...
On The Horizon For This Vessel:
-External regulation
-Alternator & volt sensing direct feed to house bank
-New batteries - most likely Firefly Carbon Foam AGM
-Solar
-More wiring modifications
-Moving the start battery out of the engine bay
EDIT: We finally cut these batteries open and discovered they were essentially starting batteries with a deep cycle sticker. The plates were no thicker than a standard starting battery. Please be careful buying your batteries and do try to treat them better than our customer did.
She is a 2007 36 footer, and was purchased by her current owner in June of 2015 in Nova Scotia, and then sailed back to Maine. At commissioning in Nova Scotia the batteries were found to be "dead". The broker ordered and had installed two brand new Costco/Kirkland "Deep Cycle" Group 27 batteries rated at 115Ah each..
One of the murdered batteries during autopsy.
NOTE: Beware this identical battery may also be wearing an Interstate branded sticker at some Costco stores.
EDIT: As shown above I recently cut open one of these batteries and found they were not at all deep cycle but rather a very thin plate dual purpose bordering on starting batteries that had a "deep cycle" sticker applied to them. Buyer beware!
I was supposed to be on the delivery trip but could not make it due to a last minute schedule change having to do with the boat not actually being ready. I walked the owner through all the things that should be checked and that could go wrong and I loaned him numerous tools for the trip. They set off across the gulf of Maine in little to no wind but they did have brand new batteries.
Deep Cycle Stickers on El-Cheapo Batteries = RIP OFF
When buying batteries please try & stick with a brand name, unless you know EXACTLY what the product really is under the re-labelers sticker. Trojan, Rolls, Deka/East Penn, US Battery, Dyno, Crown, Lifeline, Full River, Firefly, Odyssey, Northstar etc. are all reputable brands that offer deep-cycle products in their line-ups..
Sticker brands such as Kirkland, Power Star, All Rounder, Energy Master, Auto Craft, Powertron, Super Start, Maxx Marine, Cabella's, Duralast, Sportsman etc. etc. are all STICKER-BRANDS and you have little to no idea what you are really getting unless you do some extensive leg work.
I can say without a doubt, because I physically cut them open & measured the plate thickness, these batteries were not "deep cycle" and probably not even a true "dual purpose" battery, they were low budget automotive grade batteries wearing a "Deep-Cycle" sticker.
When companies slap a sticker on a battery mistakes get made and misleading marketing can rear its ugly head. Rather than go into what to look for in a deep cycle battery here, click below for more info:
What is a Deep Cycle Battery? (LINK)
Heat Murders Batteries:
When the boat got to Casco Bay I immediately went to work on her. The factory layout was horrible with both of the "new" batteries in the engine compartment. Heat murders batteries, and while this does not happen instantly heat and low SOC are not good for longevity. These batteries had already likely exceeded 125F on a few occasions. I actually measured the case temp of one of them at 117F when they came into the anchorage after a multi-hour motor in no wind. They also had to motor for approx 13 hours of the delivery trip due to zero wind. It was clear the upgrades would start with getting the batteries out of the engine space.
Seeing as budget was short but cruising plans were on the calendar, I set out to relocate the two new batteries & get them out of the engine bay. I also planned to wire the two new batteries as a hard-wired parallel house bank. I had a used but otherwise good condition group 31 battery that I gave to the owner as a "starting battery" and we left it in the engine bay for this season. In the image below there had been two group 27's and now there is just one group 31 acting as a starting battery. Still, this is a a very poor location for batteries.
Partial State of Charge (PSOC) Cyclic Use Murders Batteries:
The alternator can also be seen in the image below, as well as a number of safety flubs that needed correction, and is a bone stock Paris-Rhone automotive alternator. A shortcoming of this alternator is that it temp-compensates and reduces the absorption charging voltage as the alternator heats up. This type of temp protection for the alternator, is not at all healthy for deeply cycled batteries.
Because of the way this alternator self protects itself it leads to chronic under charging and an absorption voltage that is far to low and incredibly unhealthily for the batteries. On the list for this boat, to correct this short coming, is external regulation.
Because of the short engine run times on sail boats, and the insanely low voltages we were measuring at the batteries, these batteries were suffering from pretty harsh PSOC use.
PSOC cycling use means that we never fully recharge the bank before discharging the bank again. When we PSOC cycle lead acid batteries they suffer two things. The first is a phenomenon called "capacity walk down" which begins as early as cycle #1. The walking down in capacity is caused by the number two item, which is sulfation. Essentiaally PSOC walk-down and sulfation means or necessitates that each day you actually need to run your engine a bit longer and longer to achieve the same usable capacity. So if you charged for 1 hour per day, at a steady 40A, and assumed you were getting 40Ah back in think again. The usable capacity will continue to walk down a bit with each PSOC cycle. The only way to slow the effects of PSOC cyclic use is with frequent full charges and equalizing the batteries regularly. For more info on PSOC cyclic use, and its effects, see the May 2015 article in Practical Sailor -
Fighting Sulfation In AGM's
Incorrect and Inaccurate Voltage Readings Can Murder Batteries:
The boats analog DC volt meter was horribly inaccurate and was not working correctly. The owner checked battery voltage using the volt meter but had no idea it that was inaccurate. On battery #1 the analog volt meter was reading +0.9V off , on the high side, and for bank #2 +0.8V high. This does the batteries no favors because at 12.1V the batteries were respectively at 11.2V and 11.3V which is essentially DEAD. Discharging the batteries to this level will rather drastically shorten their usable cycle life, especially starting type batteries masquerading as "deep cycle"...
Let's Just Try and Get You Through The Season:
The two new Costco batteries were moved to a cooler location below the starboard quarter-berth, where they should have been all along, the builder even had a shelf for them already built into the hull liner.. Unfortunately the platform molded into the hull liner prohibits flooded batteries being mounted in the proper orientation so the owners next bank will be AGM.. The Costco batteries were charged and equalized briefly during this conversion. The battery cabling was all well sized by the builder, at 2/0, so new jumpers were made of 2/0. The batteries were secured and wired in parallel for a house bank. At the same time an ACR was added to charge the starting battery. Some other wiring changes were also made to make it easier for the owner to operate.
Better SOC Monitoring:
The owner was not up to installing solar this year and the boat resides on a mooring, not having solar on a mooring is a terrible situation for batteries on a sailboat..
I explained to him that I was doubtful his Costco batteries would make it into season two, but he suggested season two would have more budget for things such as solar & newer and higher quality deep cycle batteries. The choice was made to install a Smartgauge this year so he could better track SOC and help try to keep his bank healthy enough to get through the season. The Smartgauge was already part of his long term plan so installing it for this season, considering the inaccuracy of the on-board volt meter, seemed like the best fit.
Time to Decommission:
When I went to decommission the boat the owner had been running the water pump to drain the tanks. We stopped and let the Smartgauge sit for about 1 hour and it stabilized at 38% but with the LED lights on, and the stereo, the SOC kept dropping until I disconnected the bank at 34%. The owner was lamenting that the SOC had been dropping more rapidly as the summer grew on but that he had "learned" how long he could run loads, not very long..
In total he and his family did approx 25 over-nights that resulted in deep-cycling the batteries to approx 50% SOC. There were also a fair number of very deep discharges, perhaps 8-10, before the Smartgauge was installed. There were also 5-6 days of racing with the fridge running and in these scenarios they usually sailed on and off the mooring with no charging.
After the Smartgauge was installed the owner tried very hard not to let it drop below 50% SOC but as the batteries grew tired, keeping them above 50% SOC became a losing proposition. Even with a ten hour motor one weekend, from Portland, ME to Isle Au Huat, ME, with zero wind, the batteries still never reached 100% SOC, due to sulfation.
The SOC in the fall when the batteries were removed:
Testing The Bank:
This scenario created a good opportunity for me to not only test the accuracy of the Smartgauge but to also test the batteries for their current state of health.
I photographed the Smartgauge at 34% SOC then removed the batteries and took them back to the shop for testing. The batteries were wired in parallel, just as they were on the vessel, and connected to one of the Ah capacity testers. Look close and you can clearly see the 5/15 date code stickers on the batteries. Brand new as of May 2015...
I did not recharge the batteries before discharging them to the industry standard of 10.5V under their rated 20 hour load. The batteries delivered a paltry 20.22Ah's before hitting 10.5V!! This is a 230Ah rated bank so at 34% SOC it should have delivered somewhere in the neighborhood of 78Ah +/- before hitting 10.5V. I knew the batteries were in bad shape when they could barely muster 20Ah's from a reported 34% SOC..
I then fully charged the batteries and floated them for two full days beyond the absorption charging and ran a full capacity test at the 20 hour "as new" rate. The battery case temps hit a low of 74F and a high of 78F, well within reasonable for this testing. This time they delivered a measly 52.94Ah. You read that correctly, they were delivering just 23% of their factory rated capacity in just 4.5 months. A dead battery, by industry standards, is anything less than 80% of its as new factory Ah rating!! 23% is really quite murdered...
The good news is that 52.94Ah, in total capacity, compared against 20.22Ah, from the 34% Smartgauge measurement point, we were within 4% accuracy of the batteries actual physical capacity. This 4%, for a battery that has been pretty murdered, is an exceptional feat for the Smartgauge. I know of no other battery monitor in existence that could have predicted this massive decline off the abyss as accurately as the Smartgauge did.
If this had been a traditional Ah counter the bank capacity would still have been programmed for 230Ah's with an actual capacity of just 53Ah's... Think about that for a moment...
Never satisfied with "good enough" I decided to do a full equalization of 8 hours at 15.5V. The batteries were charged until current declined to well under 1A at 14.6V then the voltage was brought up to 15.5V and held there for 8 hours. I then re-tested the batteries for capacity at the 20 hour as new rate. This time they delivered 56.41Ah, an improvement of 3.47Ah. I repeated the test a second time with an additional 2 hours of equalization and netted within .4Ah. This was the most we were ever going to see out of these murdered batteries.
I also split the batteries and ran individual capacity tests. I wanted to see if one battery was the culprit or was it both of them more equally? Battery #1 tested at 28.04Ah and battery #2 tested at 28.32Ah. Both batteries were within 0.28Ah of each other, so they died pretty evenly, but they still died a pretty quick death.
This test ensured we did not have one really bad battery and one marginally good one propping the other up.
The good news? The equalization process brought the Smartgauges 34% SOC reading, and accuracy, down into the 2% range, in the real world and in an abusive environment. This is really quite remarkable.
Specific Gravity is not a good tool to determine State of Health or Ah Capacity:
To many I know this will sound like blasphemy, but save your clothes from acid burns...... How on Earth can I say that? Well for starters each of the 12 cells measured as near identical as you can get. The batteries were not out of balance in any abnormal manner. They also hit a specific gravity of 1.280 when fully charged. Yes they were "fully charged" but instead of 230Ah's they could only deliver 53-56 Ah's. Specific Gravity can tell you SOC, like the Smartgauge, but not SOH / state of health. A good specific gravity reading tells you nothing about the batteries actual capacity just its SOC, which the Smartgauge can do externally with no acid burns..
Here we have a bank delivering at best 24.5% of its advertised capacity (230Ah rated delivering 56.41Ah after EQ) in somewhere around 35-40 cycles most likely due to sulfation, being the wrong battery type for the application, a dumb alternator regulator, never getting fully recharged after each use and possibly some effects from heat.. Yes these batteries also had a few super deep cycles but any deep cycle battery should handle the occasional dip to 20% SOC with ease, if otherwise properly charged and properly selected for deep cycle use..
Lessons Learned:
*All lead acid batteries need to get back to 100% SOC as often as possible. A stock alternator on a mooring sailed boat is simply inadequate for optimal cycle life. For mooring sailed boats and battery longevity a small solar array can do wonders.
*Cheap Group 24, 27 & 31 flooded batteries are not deep-cycle just because the sticker says so. I have a good hunch these are actually starting batteries not even dual purpose, but they wear a "deep cycle" sticker.
*Due to the liner pan and clearance, the batteries were mounted in an improper orientation for the cells/plates on a sail boat. The vessel design precludes proper orientation of a sufficiently sized flooded house bank without doing some serious $$$ modification.
*The label on these batteries is likely a complete and utter hip shoot. I find it hard to believe that these batteries could have ever delivered 115Ah even when just barely broken in. They faded so fast in Ah capacity that I've only seen this once before, and they were starting batteries that had been mislabeled by a regional distributor.
*These batteries weigh considerably less than a Trojan group 27 so they are likely closer to a starting battery than a dual purpose.
*Unless you are getting 14.4V(bare min for flooded batteries), at the battery end of the charging circuit, but preferably 14.6V to 14.8V, you will wind up chronically under charging and will kill your batteries earlier due to sulfation. The absorption stage of charging is the healthy part where the lead sulfate is reconverted. If you never attain an absorption voltage, due to voltage drop and an unsuitable alternator design for a cycling bank, then the batteries will die sooner than later. In this case murdered in one short 4 month season.
*Sulfation murders batteries quickly, if you allow it to. Batteries need to get back to 100% SOC as soon after a discharge as possible. This simply does not happen on most sailboats with alternator only charging.
*Heat kills batteries. While the effects of heat are not instantly murdering batteries lead sulfate hardens and becomes un-reconvertable faster in warmer temps than it does when batteries are kept cooler. Deep cycling and heat do not play well together.
*If you are on a mooring solar or wind charging is going to be pretty critical.
*If you want to know your SOC the Smartgauge actually works and is very simple for the average boater to understand.
*Inaccurate voltage readings can actually lead to a worsening of the battery condition. Analog volt meters can be horribly inaccurate in the marine environment so please compare these readings to a meter with known good accuracy.
*Specific gravity readings tell you nothing about state of health or Ah capacity only SOC. The specific gravity readings on these batteries showed them in good balance and showed them attaining a full charge yet that full charge lacked any real stored capacity...
On The Horizon For This Vessel:
-External regulation
-Alternator & volt sensing direct feed to house bank
-New batteries - most likely Firefly Carbon Foam AGM
-Solar
-More wiring modifications
-Moving the start battery out of the engine bay
EDIT: We finally cut these batteries open and discovered they were essentially starting batteries with a deep cycle sticker. The plates were no thicker than a standard starting battery. Please be careful buying your batteries and do try to treat them better than our customer did.