Behavior of marine batteries

jssailem · May 25, 2021

Fredct said:
Should I change both including the new one that is 2 years old?

Batteries are funny beasts. When your 5year old battery started to die (no autopsy many causes) the “newer” one tried to help its buddy. Lending it power instead of giving it to your boat circuits. In essence sacrificing itself to keep the 5year old around.

Buying one new battery will restart the process of killing the new battery to help the 2 yr old.

You can test the 2 yr old battery using the 20 hour battery stress test described by MaineSail on his website. What is a Deep Cycle Battery? - Marine How To

Knowing the ability of your charging systems to keep your batteries doing their thing, will help you get the most out of your batteries abilities. Feed them properly will let them live longer.

Ward H · May 25, 2021

Fredct said:
Clarification. We have 2 batteries (1 and 2). One 5 years old, other 3 years old. We have AC charger which we leave on for days on end. We save #1 for emergency when on water and run everything else off of #2 (autopilot, VHF, lights, water pump). i would call us miserly for energy but I am not sure how much the autopilot at idle consumes.

I believe several comments answered your questions.

Suggestions made are for upgrading your system are good ones but I believe your current system is adequate for what your doing now. After all, you already diagnosed your problem, an aged battery.
And thats why you keep #1 in reserve. Your system worked fine for a day sailor who occasionally overnights.
Having a portable battery pack for charging the portable devices separately from the boat batteries is a good idea.

If you do want some Ahrs in your house bank, my suggestion for an upgrade would be to measure the battery compartment and see if you can install a Grp 31 battery as the house bank and a Grp 24 as the reserve. You’d be shifting a few Ahrs from your reserve to your house bank.
If they would fit you might be able to swap the new uninstalled battery for the Grp 31.

Good Sailing

dlochner · May 25, 2021

Fredct said:
Thanks for all the help.

I am lost on one point. We are NEVER running both batteries at the same time except when running the engine (so charging). Our house is #2 and our starter (or emergency) is #1. Using the batteries in parallel will effectively have us running on ALL at all times. May be gentler on the batteries but we would lose the safety of the starter battery. Pb batteries are not expensive in the grand scheme so I don't mind changing one every year or other year and knowing that I can start the engine in the morning.

A improved and not that expensive option is to use an Automatic Charging relay (ACR) between the house and start/reserve battery and then run all charging sources to the house battery. This will keep both batteries charged, without paralleling them and reduce the amount of switching from 1 to 2 to both. There is an article on MarineHowTo.com on the ACR.

When the battery switch is on both, the batteries are paralleled and the points Scott and John brought up with the weaker battery sucking power from the stronger battery does come in to play while the switch is on both and there is no charging source. Depending on the difference in charge states between the 2 batteries the energy exchange can happen quite quickly.

Stu Jackson · May 25, 2021

Dave explained it very well. Here's the longer answers: They all come from my
Electrical Systems 101 Electrical Systems 101

***************************
OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009

)
1/2/BOTH Switch Considerations

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings

This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation

What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
Battery Switch Question ? and Battery isolator / voltage regulator / batteries

Making Sense of Automatic Charging Relays (2019)
Making Sense of Automatic Charging Relays - Marine How To

Scott T-Bird · May 26, 2021

In my opinion, I think that running all your house loads on one Grp 27 is inadequate, if you are going to be cruising and staying overnight on your boat at anchor. That is the reason for my suggestion that you make a larger house bank with 2 new batteries. As Dave responded, the best way to do that is to buy 2 new batteries for the reasons he stated. My only thought about the power pack is that it would be unnecessary if you use your newish 2-year old battery for reserve. Space for batteries is always an issue. Perhaps you make space, perhaps you use one Grp 31 as Ward suggests (it would not give you as many ah as 2 grp 27, I think). Perhaps you can live with a single grp 27 (new) and your 2-yr old batt for reserve/start. Obviously, there are choices to decide upon.

I would learn more about your charger/inverter, if I were you. I know those things are very expensive; hence, I would never buy one. But since you already have it, you can make the best use of it if you can, I suppose. Inverters are not very efficient (relative term), that I think I know. If you are going to settle for a very small house bank, you wouldn't seem to get much use from the inverter. Perhaps you get just enough to make you happy. There are so many issues that are all linked together. You can simply buy a new battery and get along as you do, but then why the question?

Kings Gambit · May 26, 2021

I struggled for several years keeping my batteries up at anchor if anchored for more than a few days, the chief draw being the reefer. After a few exchanges here with our experts I reconfigured my power system as now comprised of four 6-volt “true” deep-cycle batteries which I bought new together, wired in series-parallel to combine two 12-volt units with about 460 amp-hr, added two 80-watt solar panels of which I typically use only one at a time, but can use both (a bit unwieldy), and installed a Balmar high-output (150-amp) alternator /external regulator & temp gauge. Whenever the batteries drop to near 12 v, I charge for 1/2 hr @ 3,000 rpm on the alternator (1500 rpm on the diesel), which lasts several hr. I now rarely go more than an hr a day charging w/the diesel, and can lay at anchor indefinitely w/o power issues as long as we maintain our daily conservative use of power. Of course, I’ve swapped out most of the lighting for LEDs including the anchor light atop the mast, plus we have an oil lantern good enough for functional lighting in the salon, but not reading.

So. My advice is to follow the advice you’re getting!! Your power issues should fade away.

Scott T-Bird · May 27, 2021

I didn't mean to harp on he inverter thing as it seems that you don't use it. It must be a legacy that came with the boat. But I do think that you should look closely at the performance of your charging regimen. Your short time motoring is not charging either battery adequately. It doesn't matter if you set the selector switch to Both, 1 or 2 ... the alternator is not running long enough and it probably is incapable of keeping the batteries charged, even if you increase the time of engine running.

You seem to indicate that you leave the selector switch on Both for AC charging. I'm not sure why that matters, except are you saying that when you leave the boat with the charger running, you leave the switch on Both? It should be off, I think. Maybe I misunderstood what you said in #25 above. If you are combining your batteries when you leave the boat, that doesn't sound like a good idea to me. :huh:

Your AC charger should be independent from the selector switch. I don't know why it would be wired thru the switch. That said, you should know how the charger works and make sure that it is charging both batteries, either with an ACR, echo charger or the newer chargers can be wired directly to individual battery banks. Know how yours operates! Maybe if you do what I think you do, it is an accepted practice, but it doesn't sound right to me ... I'd be interested to know.

It sounds like you have a history of changing out batteries. If you are expecting to replace a battery every season or two, just for the comfort of having a reliable battery for starting your engine, you may be killing your batteries unnecessarily simply because your equipment is not set up to charge the batteries adequately. You can go along like that if you want, but it is wasteful.

Starting your engine takes hardly any power and the power consumption from starting your engine isn't really a valid reason for using your reserve battery for starting. If you want a reserve battery for that peace of mind, then just keep it on the side, fully charged, for reserve. All that switching back and forth to start the engine and then use your house battery is just not necessary. That said, a single grp 27 is not adequate for a cruising sailboat used for overnights.

If you really want to start your engine from a separate battery and have the comfort of a reliable starting battery, there are better options than the ubiquitous 1+2+Both selector switch, but I don't want to go into that unless you do!

BTW, what is a "false anchor alarm" and why did they cause you to start your engine twice during the night? I don't really follow that. :huh:

BarryL · May 27, 2021

Guys,

I don't mean to speak for the original poster, but his use case is about as simple as can be. From his original post:

Background: We are the habit of turning on engine, motoring for 10 minutes or so and then sailing with selector to #2 (drain is limited autopilot, VHF and Navigation). At the end of the day, we start engine from #2, dock, plug in and all is well. On a recent adventure, we anchored overnight, running lights and water pump sparingly (all on #2). Two false anchor alarms forced us to restart the engine at night. In the morning, battery #2 read 10 volts and could not start the engine. We were fine with #1.

---
So the boat is MOSTLY used for day sails. When not sailing, the boat is at a dock, connected to shore power, and has an onboard battery charger.

So, unless the OP starts making plans for a bunch of multi day trips that will be spent at anchor, there is a really no need for any changes to his electrical system. Even a single group 27 battery can provide enough power for a night at anchor. This would include the anchor light, some cabin lights, and perhaps a radio for entertainment. I do agree that combining two group 27 batteries into a single bank would be 'better' for the batteries, as long as there is a way of starting the engine if something happens and the two battery bank becomes disabled.

BTW, my last boat had 3 batteries onboard, 2 for the house bank and 1 for the engine start. They were connected to the standard 1 - 2- both - off switch. The onboard battery charger was connected to the same switch, so whichever battery was selected got the charge from the on board charger. So if I was in a slip with shore power, the batt switch would be set to 'both' and the battery charger would be on. When on my mooring, the switch would be set to 2 (house bank), or 'both' if the engine was running. At the end of the day, if I could not start the engine with '2' house bank I would switch to 1, start the engine, and then back to BOTH to charge all the batteries. This worked fine for the 8 years I owned that boat.

My new boat is much more complicated, with ACR, isolators, 7 batteries (1 for engine, 4 for house bank, 2 for bow thruster) and I am learning more about how all that works.

Barry

Ward H · May 27, 2021

Scott T-Bird said:
Starting your engine takes hardly any power and the power consumption from starting your engine isn't really a valid reason for using your reserve battery for starting. If you want a reserve battery for that peace of mind, then just keep it on the side, fully charged, for reserve. All that switching back and forth to start the engine and then use your house battery is just not necessary.

@Fredct
I fully agree with Scott's statement above. If you don't use the reserve battery, you do not need to charge it every time you motor or plug into shore power for the battery charger. An good, unused, fully charged battery will hold its charge for quite some time. You probably only need to put it on the shore power charger maybe once in the middle of the season. Do not worry about charging it from the alt.

I also think if you are frugal with your house bank usage and only overnight once in a while you will be fine with your Grp 27. Maybe replace some lights with LEDs, use the battery pack for charging devices and if you find you need to use the reserve battery to start the motor after an overnight, then consider improving your system.

Until then, your recent issues were most likely the aged battery and you are already replacing it.

PS: @BarryL posted while I was writing. I agree with his post.

dlochner · May 27, 2021

Fredct said:
Our SOP when we encounter an anchor alarm is to fire the engine, pull the rode in and then reset the anchor by reversing the engine. till full scope is reached and the line is taunt. I can't imagine doing that any other way. We encountered two alarms in a single night and battery #2 was low in the morning, leading to the question about power consumption during engine start.

Perhaps a new modern anchor would be in order. But that's a topic for a different thread. :beer:

Tally Ho · May 27, 2021

On the 1-2-Both-Off switch and the charger…I thought that MaineSail mentioned many builders wired the charger output to the C post…
1) doesn’t that mean the switch can be on any position except “Off” and any battery connected through the switch will be charged?
2) If not, how would you wire the charger output to the switch?
3) If you have a 2-bank charger, and hooked up a charging source to A and B (or 1 and 2) positions on the switch, what happens when you switch to Both?

I just replaced 2) 6-year old group 27 marine batteries wired as individual banks on my battery switch. One would drop to 10 volts within an hour of taking it off the charger…the other dropped to 10.5 v. I set up 2) 215 AH 6-volt golf cart batteries as the house bank (Just 215 AH for the bank in series). I am working on a place for a start battery in case I do something stupid and run down the house bank.

But I am also trying to figure out how to charge it…
I have an older 2-bank charger. 1) bank charges at 10 amps…the other at 5 amps. I am still tracing to see where these charging wires go….I assume at least 1 goes to the C post on the switch. I suppose 1 could go to the A post and the other to the B post…but do they combine when switch to Both? It is a Guest Model 2614.

There are no wires connected to the batteries except the bilge pump. But there seems to be a lot of stuff on the battery switch…

Always something to learn! The change to 6-volts wasn‘t too hard.

Greg

Scott T-Bird · May 28, 2021

Fredct said:
On shore power, boat is plugged in and selector to OFF. Underway, the selector is set to ALL. This is how we learned to sail but writing this makes me think that perhaps both batteries charge at the same time no matter what I use on the selector. Need to be examined further.

Our SOP when we encounter an anchor alarm is to fire the engine, pull the rode in and then reset the anchor by reversing the engine. till full scope is reached and the line is taunt. I can't imagine doing that any other way. We encountered two alarms in a single night and battery #2 was low in the morning, leading to the question about power consumption during engine start.

On a vessel that is 40+ years old with at least 5 owners, it is not straightforward to reconstruct what goes where for what purpose. The charger and inverter are the newest components and the wiring has been redone (not by me). This all throws me back to the bad battery at the end of its life.

I hear you about not knowing exactly what the previously owner has done. We purchased last year and I am still a little fuzzy about the wiring, even tho our P.O. left some pretty detailed records. Our battery charger is wired to the house bank, with an echo charger to charge the reserve. All I know for sure is that I don't have to leave the selector switch on (in any position) to charge batteries from shore power. Everything has been working ok for me, so I have not really dived into any modifications or traced all the leads.

If the builder or owner runs the shore power charging current thru the "C" post on the switch, I think that is a different story - then the switch would need to be on one of the positions. I'm not necessarily convinced that it would be common practice among builders. That seems odd to me. I never had an on-shore charger until I bought one for my previous boat a few years ago and I wired it as recommended, which wasn't thru the selector switch, for sure.

As you may be aware, I pay attention to words when I read. So when you wrote "false anchor alarm", I'm thinking so if you have a false alarm then why are you re-setting your anchor? I guess what you really meant is that you dragged anchor twice in the night. That's not good. It may lead to another discussion!

Scott T-Bird · May 28, 2021

Fredct said:
As far as charging goes, there are 2 scenarios. On shore power, boat is plugged in and selector to OFF. Underway, the selector is set to ALL. This is how we learned to sail but writing this makes me think that perhaps both batteries charge at the same time no matter what I use on the selector. Need to be examined further.

I think that it does matter how you use the selector switch. First, understand the switch ... it has 3 posts - there are 2 sources (batteries) and just 1 output - the starter and the house panel combined. If this is basic to you than I am very sorry about the explanation but it often seems that confusion over some of these issues stems from misunderstanding of the switch.
The "C" post is the output post. The "A" and "B" posts are the source posts (from each battery). Your alternator positive lead is <probably> connected to the positive post on your starter. From there it is back-fed to the "C" post. (Your starter and your house panel are both connected to the "C" post - the output or load post). You have to select the source(s) with the selector switch (either 1, 2 or B) in order to connect & charge the batteries as desired. In the OFF position, neither of the batteries are going to be connected to the alternator charging source.

IF your shore charging source is connected to the "C" post, then you must use your selector switch to direct the charge. In an earlier post, you seemed to suggest that you used the BOTH position when shore charging. In your last post you seemed to indicate that you leave the switch OFF when shore charging. To be clear, you need to know how the charging sources are connected (both the alternator and the shore power). Many of our comments are based on assumptions of how the charging sources are connected. The assumptions may be incorrect, so it is necessary for everybody to be clear. There are multiple wiring diagrams for charging sources. For instance, @BarryL indicated that his shore power source did run thru the C post on his switch, therefore he did have to select a position on the switch to direct charges. I really don't know how common this is since I've never had it done this way, but if that is the case on your boat and you turned the switch to OFF when you leave the boat with shore power on, perhaps you weren't charging at all.

The battery you were using for starting probably stays healthier because it doesn't really discharge at all and the charging you get by running the engine for short periods probably gives you enough to keep it topped off (or nearly topped off) - like a car battery, it is only used when the engine is on. But the battery you use for house load may be chronically undercharged if it isn't getting a solid source of charge.

jssailem · May 28, 2021

Fredct said:
I feel moderately confident that the one battery replacement will fix issue in the near term.

That is good.
There is perfect and there is satisfactory. Unless we are talking brain surgery where I want perfect if I’m under the knife ( I think). With a boat often times satisfactory is good enough to go sailing.

I noted you said you have no idea what all the other owners have done. I get that. You really don’t need that information. My thoughts are you only really need to know how the boat is wired right now. With out this knowledge you are left to guess at solutions to problems. You may need to get dirty and identify all the wires and what they do or are connected to.

Relying on the charge/inverter to fill the battery well while connected to shore is ok. For battery health this may mean at least 24 hours of shore power. That’s a SWAG cause no data has been provided about the shore power charger.

30 minutes of intermittent alternator connection (assume as previously suggested 15 minutes to get to sailing and 15 minutes to get to slip) to the battery is not enough to keep the batteries functioning at a high capacity.

How you use your boat is all that matters. Having the power to do that and a way of storing that power on the boat should satisfy. If buying batteries every couple years let’s you do that and does not break the boat budget all the better.

Enjoy the sailing.

jssailem · May 28, 2021

I feel your pain. I’m still crawling into and back out of voids on my boat.

I am heading to the boat in an hour. Removing 6 of the windows to refurbish. After 48 years the caulk sealant holding the glass in the frame is breaking down. More fun.

Selector	Shore power switch	Shore power	Result
OFF	ON	ON	Charging
ALL	OFF	ON	Draining both
OFF	OFF	ON	Draining both
ALL	OFF	OFF (Engine ON)	Charging both
2	OFF	OFF (Engine OFF)	Draining 2
1	OFF	OFF (Engine OFF)	Draining 1
ALL	OFF	OFF (Engine OFF)	Draining both