Battery Geriatrics

[Roger Long]

OK, now that we know that I'm not the person to ask about batteries

http://forums.sbo.sailboatowners.com/showthread.php?t=128420

and am about to head out on a long cruise to remote places with two AGM batteries that are probably on their last legs, what do I look for and how do I make a decision about whether to replace them proactively?

Voltmeter reads a hair under 14 V. when engine is running. Batteries read about 13.8 V. when first checked after main switch being off for 12-24 hours. I've almost never seen voltage below 13 spot checking while cruising. Engine always starts as fast as a car. I run both batteries together BTW and am just very careful about loads.

I plugged shore power into the boat a couple days ago after using the batteries for lights and running a vacuum. It had been sitting all winter. The charger went through its 3 cycles in about 5 minutes to maintenance level. Voltage 13.8.

Will I just wake up some morning in some remote place and find that everything is dead or will I see some change in these characteristics that will warn me that trouble is coming? A battery monitor isn't in the cards this year as I've spent too much. It's hard to justify anyway with my modest electrical usage.

If I just put my Harbor Freight battery tester (the one with the loading gizmo in it) on each battery, will that tell me anything useful?

 

[seadaddler]

Wet Cells

Well don't know if this will help but I just replaced my 2-4D's with 4 6 volt T105 Trojan and so far love them after a 2 week cruise.
Any way my first clue was coming to my boat at the Marina plugged into shore power and the boat had a bad smell of battery gasing and when I checked the batteries they were cooking,I checked them with a battery meter like yours and one said bad and one was good but a day later they checked both bad just junk for sure.
Good Luck and hope you do OK.
Nick

 

[Philip_Oceanis 361]

I run both batteries together BTW and am just very careful about loads.

I am not a battery expert but this definately is not very good. You are simply pushing your luck! Keep engine and services batteries separate with the option to connect them with a switch in case of emergency. Alternatively, at least have on board a jump start (I think it's called like this).

 

[Roger Long]

this definately is not very good.

I carry a portable jump start battery which will start my small engine in a pinch. The only thing running when I go to sleep at night is the LED anchor light and sometimes a small GPS plugged in for an anchor alarm.

I prefer the slight risk of drawing everything down to doubling the discharge level of my batteries.

If I had refrigeration or other big electrical draws, I would certainly have a separate starting battery.

 

[Maine Sail]

Roger,

The best test is to do a 20 hour load test for capacity.

If your batts are 115 Ah then you'll want to apply a 5.75 amp load and monitor when the voltage drops to 10.5 volts. New batteries should go 20 hours before hitting 10.5 volts. When you get out to 16 or so hours begin checking the voltage. You can use a dimmer switch and some light bulbs to get your 5.75 a load dialed in. Test each battery separately.

I can also throw them on my analyzer which will measure CA and voltage and can give an approx "condition" assessment but nothing beats a true 20 hour capacity test.

To figure the load you need to apply take your battery amp hour rating and divide by 20.

 

[Stu Jackson]

I'm surprised MS didn't give you the AGM battery "lecture." http://forums.catalina.sailboatowners.com/showthread.php?t=124973

If I were you (wish I was comin' along!) I'd go for good wet cells, and avoid future problems. Best bang for the bucks.

I've mentioned this before, but I knackered my three wet cell house bank batteires when i broke my leg skiing two years ago 'cuz I left them uncharged for too long. Learned that valuable lesson that the blogs and research material are right on! From MS's AGM analysis, I would think twice baout depending on them.

Also, don't forget this gem: www.amplepower.com, tech tab, download the Ample Power Primer.

 

[Roger Long]

I'm surprised MS didn't give you the AGM battery "lecture." http://forums.catalina.sailboatowners.com/showthread.php?t=124973

If I were you (wish I was comin' along!) I'd go for good wet cells,

He did in the link on the link I provided. That's what I meant by not being the one to ask about things like batteries.

I'll get back to you all after I have a chance to run the test he describes on each battery. I won't be surprised to find that they are fine as I hardly draw them down at all in use. I'll be equally unsurprised to find that I need new ones.

I'll probably be converting all of my remaining inside lighting to LED with the now available swap in bulbs. At that point, there won't be much nighttime load at all. That should offset my anticipated lower diesel operation. I'm also starting to think about where I could mount a solar panel.

I still don't want wet acid in my boat. Having a battery location where I can't get my face far enough from the batteries to see anything or back out quickly is a factor for me. It's a structural battery box in about the only feasible location.

 

[Stu Jackson]

Understood. I had a dockmate with a Mason 33, and they put the batteries where he even couldn't find them for altogether too long!

 

[Philip_Oceanis 361]

Roger,

The best test is to do a 20 hour load test for capacity.

If your batts are 115 Ah then you'll want to apply a 5.75 amp load and monitor when the voltage drops to 10.5 volts. New batteries should go 20 hours before hitting 10.5 volts. When you get out to 16 or so hours begin checking the voltage. You can use a dimmer switch and some light bulbs to get your 5.75 a load dialed in. Test each battery separately.

I can also throw them on my analyzer which will measure CA and voltage and can give an approx "condition" assessment but nothing beats a true 20 hour capacity test.

To figure the load you need to apply take your battery amp hour rating and divide by 20.

I am afraid to ask this because it will be probably a stupid question.....But anyway, here it is: Doesn't this 20 hour load test kill the battery? You are not suppose to discarge a battery completely, I think.

Thanks

PS: Despite having a simple battery monitor (a NASA) and measuring amp used I would also like to do that test and find out about the condition of my batteries.

 

[Roger Long]

Doesn't this 20 hour load test kill the battery?

If it goes completely flat in the 20 hours because you are not monitoring the voltage then, yes, you've killed it. If it reaches the 10.5 volts much before the 20 hours, then it needs replacement anyway.

I will time the test so that I can check the voltage about every hour after the first eight (overnight) and then graph the time vs. voltage. I may be able to see a trend before it gets as low as 10.5 volts that will tell me what I need to know.

 

[JohnShannon]

Most of the battery manufacturers have spec sheets and charging suggestions and test methods on their web sites. So you can see exactly how they determine capacity, and it is like MS said, fully charged battery discharged at a 20hr rate with a cutoff voltage.

The voltage of the battery while it is being charged is not an indication of health, you could for example remove the battery (which would reduce the capacity to zero) and still see 14.1V coming from the charging system. So that isn't a good indication.

Load testing is what is required. If you don't have the patience for a 20hr test you can up the load, but be aware that the Ahr capacity will be reduced somewhat. That info should also be on the battery datasheet.

 

[Roger Long]

The voltage of the battery while it is being charged is not an indication of health

Correct. I was mentioning it because I know my system hasn't been charging at 14.5 or more as some alternators will do because of manufacturing variations. Charging over 14 volts will hurt AGM batteries.

 

[Maine Sail]

Charging over 14 volts will hurt AGM batteries.

Charging over 14.1 volts will hurt many if not most GEL batteries but not AGM unless the temp is in the 120 degree range which in and of itself is really bad for the batts to begin with.

Most current AGM bats can be charged at similar voltage levels to wet cells but not GEL. Trojan AGM's do have slightly lower AGM charge voltages than Lifeline & Deka though.

DEKA AGM MAX Absorption Voltages
Less Than 40 F Max Charge Voltage = 15.4V
40-50 F Max Charge Voltage = 15.1V
50-60 F Max Charge Voltage = 14.9V
60-70 F Max Charge Voltage = 14.75V
70-80 F Max Charge Voltage = 14.6V
80-90 F Max Charge Voltage = 14.4V
90-100 F Max Charge Voltage = 14.3V
100-110 F Max Charge Voltage = 14.2V
Greater Than 120 F Max Charge Voltage = 13.9V

 

[Roger Long]

but not AGM unless the temp is in the 120 degree range

I'll have to stick a thermometer in my battery box. Mine is in the engine room right next to the engine so I'm glad to see my charging voltages right about at 14.

I thought I'd seen a reference in your section about the AGM setting on a particular charger being 14 volts. I guess I'm due for a complete review of this subject.

Say, how exact does the amp draw have to be on a 20 hour test? If I have light bulbs that total the draw at their rated watts will that be close enough or do I have to be spot on?

I'm getting very interested to see what the results of this test will be and hope to get to it soon.

 

[Maine Sail]

I'll have to stick a thermometer in my battery box. Mine is in the engine room right next to the engine so I'm glad to see my charging voltages right about at 14.

I thought I'd seen a reference in your section about the AGM setting on a particular charger being 14 volts. I guess I'm due for a complete review of this subject.

Say, how exact does the amp draw have to be on a 20 hour test? If I have light bulbs that total the draw at their rated watts will that be close enough or do I have to be spot on?

I'm getting very interested to see what the results of this test will be and hope to get to it soon.

You want them to be pretty close and also the temp should be around 77F which is what they are rated at. Also once light bulbs warm up the amp draw often change slightly. You may also call DEKA and see if they have a 5 hour rate that they don't publish. On the group 24, 27. 31 etc. the only publish a 20 hour rate.

 

[Roger Long]

. You may also call DEKA and see if they have a 5 hour rate that they don't publish.

Are AGM batteries one of those things that are all made by the same company, DEKA, and then re-labled by others? I can't remember what mine are (I sure hope they, or at least the Amp-hours, are labled on top) but I bought them at a battery store instead of a marine store. DEKA doesn't ring a bell.

I wish I had a better idea about what this test is likely to show. If I have to take the batteries out of the boat, a bitch of a job on mine, I'd obviously rather do the test in the comfort of my home and at the correct temperature.

How linier is voltage drop? If I were to just leave about the right number of cabin lights on overnight could I get a rough idea to guide further testing? If I go down the next day and the batteries are dead, I'll have answered my question

 

[Maine Sail]

Are AGM batteries one of those things that are all made by the same company, DEKA, and then re-labled by others?

No but DEKA or more correctly East Penn is a big supplier & re-brander. Most all the WM batteries are DEKA. There are many more manufacturers of AGM batts such as Lifeline, Trojan, Optima, Northstar, Sonnenschein and others..

 

[Stu Jackson]

Roger, Balmar's website includes manuals for their regulators, which include pretty good basic charging requirements for different battery types: http://balmar.net/PDF/mc-614-manual.pdf Bottom of page 12.

The Ample Power Primer, which I think I mentioned earlier, discusses how to use low loads, as Maine Sail suggests, for what you're trying to do. Rather than doing it overnight, you may choose to do it during a full day when you're on the boat and can watch the amp draws. I'm sure you could find something do during that day...

 

[Roger Long]

The Ample Power Primer,

Holy Cow Batman! I just skimmed through it

http://www.scribd.com/doc/36996296/Marine-Ample-Power-Primer-Good-for-Battery-Info-2008

I had no idea there was so much to it. I've been treating my electrical system like most people treat their fuel system and just haven't had the wake up call of the electrical equivalent of a clogged filter yet. I smell an expensive new hobby and obsession coming on.

Unfortunately, I may have spent that money for this year

 

[plaineolde]

Hi. New member here, but some may have seen me under the same name on the Catalina 36 forums.

I see a lot of discussion re: wet cell vs. AGMs. I have a pair of 4D GEL cell batteries, which I had installed around the year 2000 (may have been '99). I installed an Ample Power alternator and battery monitor/charging system at the same time, and use the factory battery charger (set to gell cell) at the dock.

Those batteries are going into at least their 10th season. I've yet to notice any degradation in their capacity. Am I extraordinarily lucky? Granted, I'm primarily a weekend sailor, so they sit on the charger at the dock much of the time. But I've taken week long cruises recently as last year, and the batteries and charging system seem to be just fine. I have refrigeration, TV, anchor light and the usual electronics. I try to run the engine an hour in the morning & evening if out for more than one overnight; it pumps in about 85 amps to start decreasing a bit over that hour.

Curious if my experience is unusual.