Two AGM in Parallel. One gets warm.

[allendick]

> Just charge both, immediately disconnect and let them sit. Measure voltage in a few hours. The one that stays charged is the good one.

Did that. They both hold charge, but sit at slightly different voltages when disconnected and one heats a bit on float.

In parallel there is a 0.5 amp loop current.

[s/v Jedi]

Originally Posted by allendick

> Just charge both, immediately disconnect and let them sit. Measure voltage in a few hours. The one that stays charged is the good one.

Did that. They both hold charge, but sit at slightly different voltages when disconnected and one heats a bit on float.

In parallel there is a 0.5 amp loop current.

First repeat the test with the other battery.

In case it tests the same: put both in parallel service again. Now run them really down with the charger off. 11.0V. Then fully recharge them while checking temperature.

It may be that they just need to be exercised like that. If you notice a reasonable improvement, repeat that deep cycle one or more times.

For possible switch to Lithium: what charger, inverter etc. do you have? Also, does your alternator charge a separate start battery? Do you wish to charge the house battery from the alternator?

[allendick]

Here is some info from LifeLine

[allendick]

They have been deeply cycled several times lately and fully recharged.

I think that I'll condition them according to instructions, but first I am seeing what they can deliver independenty (see above).

As for lithium, it seems I am good to go with drop-in LiFePo.

The start battery is a just a group 24 car battery. The house and start are connected by a Blue Sea SI-ACR. The alternator is managed by a Balmar ARS-5 regulator. Solar is a late model Victron BT. The boat is a an Oceanis 351.

[s/v Jedi]

Originally Posted by allendick

Here is some info from LifeLine

I got a feeling that you have about half their capacity left. Try the deep cycle to see if it improves.

[allendick]

Yeah. My guess is that one is doing all the work and it is time to get lithium. Problem is finding them here for a good price but my crusier community is very helpful and many have switched so I just have to do some research.

[s/v Jedi]

Originally Posted by allendick

Yeah. My guess is that one is doing all the work and it is time to get lithium. Problem is finding them here for a good price but my crusier community is very helpful and many have switched so I just have to do some research.

Here… they sell 2-packs of these too: https://www.litime.com/products/liti...00a-bms-5888wh

[Captain Bill]

I once had a battery with similar problems and it was diagnosed as an internally cracked battery post. I have also had an internal short in a pair of lifeline agms. The shorted battery reached 186F before I got it disconnected. It was at 174F when I happened to step on the cover to the battery compartment and it was hot. I was lucky I got to it when I did as it rose the last 12 degrees in less than 10 minutes. Concord said it was arcing internally. Another few minutes and it would have started boiling. Your symptoms seem more like the cracked battery post. That battery never got seriously hot but neither would it carry much of a load. Under low or no load it seemed perfectly fine.

[allendick]

11:45 15A 12.06 V
12:10 13A 12.11 V Could not power the microwave.
12:45 15A 11.98
13:55 18A 11.7 V
14:40 14A 11.75 V
16:05 14A 11.3 V I put on 750 W heater and the inverter dropped out
Even on low, the heater dropped the voltage too much.
17:05 13A 11.4 V
19:00 16A 10.7 V
19:30 16A 10.3 V
Ended experiment. Isolated battery. Voltage went to 10.7
The battery is at 26 degrees. The idle battery reads 24 degrees
8 hrs at 15 A is 120 AH

Charging now at 13.8 V and 40A

[allendick]

11:45 15A 12.06 V
12:10 13A 12.11 V Could not power the microwave.
12:45 15A 11.98
13:55 18A 11.7 V
14:40 14A 11.75 V
16:05 14A 11.3 V I put on 750 W heater and the inverter dropped out
Even on low, the heater dropped the voltage too much.
17:05 13A 11.4 V
19:00 16A 10.7 V
19:30 16A 10.3 V
Ended experiment. Isolated battery. Voltage went to 10.7
The battery is at 26 degrees. The idle battery reads 24 degrees
8 hrs at 15 A is 120 AH - Nominal capacity 255 AH

19:45 Charging at 13.8 V and 40A
20:20 36A 13.86V
21:20 29A 13.96V

[allendick]

Jan 5: Load test on the aft battery -- the one that remained cool.
Both (in parallel) have been on float continuously for days.
When disconnected this one dropped to 12.66 OCV. The other stayed at 12.82 OCV.

11:40 Load applied.
11:45 15A 12.06 V - S/B fully charged?
12:10 13A 12.11 V Could not power the microwave.
12:45 15A 11.98 V
13:55 18A 11.7 V
14:40 14A 11.75 V
16:05 14A 11.3 V I put on 750 W 110V heater and the inverter dropped out
Even on the low setting, the heater dropped the voltage too much.
17:05 13A 11.4 V
19:00 16A 10.7 V
19:30 16A 10.3 V
19:30 Ended experiment. Isolated battery. OC Voltage went to 10.7 V
The battery is at 26 degrees. The idle battery reads 24 degrees

8 hrs at 15 A is 120 AH - Nominal capacity 255 AH - Capacity is around 47%.

19:40 Put it on charge
19:45 Charging at 40A and 13.8 V
20:20 Charging at 36A 13.86V
21:20 Charging at 29A 13.96V
Left it on charge overnight.

Jan 6 7:00 AM Voltage on float charge is 13.36
7:40 Removed charger 12.77 OCV No load
7:40 12.47 with 8 amp load
7:45 12.43 V 4.4 A
7:50 12.12 V 17A
8:30 12.10 V 13A
9:30 Dropped to where the inverter quit.

Verdict: This battery is NFG. I may try equalizing but that is a faint hope.

[GrowleyMonster]

Originally Posted by allendick

I have two GPL-8DL batteries in parallel.

They are of uncertain age, but I have used them for 4 years here in Mexico. They seem to have reasonable capacity still but I have not tried to measure.

The boat sits at a dock with the 110V charger on float, and a solar system on float as well. I believe the charger settings for both are correct.The Heart monitor shows 1.8 Amps charge at the moment. The positive lead goes off one and the negative off the other so that should not be a cause of imbalance.

My concern is that today I noticed one battery is noticably warm to the touch at 36ºC. The other is at 29ºC, and the inside of the hull where they sit is at 24ºC.

This implies to me that one battery is discharging through the other in a loop and that one battery is defective.

Am I correct in assuming it is time for new batteries?

If so, the easiest thing physically is to just replace them with similar new batteries, but I am wondering if I should do that, get golf cart batteries, or consider one of the newer sorts -- carbon foam or lithium?

I will assume that you check your connections on a regular basis as part of scheduled maintenance, and keep them clean and tight, and your cables are good, and of sufficient size.

The obvious thing to do is isolate the batteries. Charge and use just one and see what your typical charge current is, and what resting voltage is, maybe do a full load capacity test. But on the face of it, it sounds like you have a bad cell in one battery.

Best practice would be to replace both. If you have room, you could set up the oldie but goodie one as a separate bank for coms, emergency lighting, alternate start battery, whatever.

The same size factor of course has advantages in that you can just drop the new ones in and hook them up, project complete in short order. You will want a helper. 8D are pretty heavy and awkward to handle.

Lithium ion and particularly LiFeP04 are gaining in popularity, and their safety record has improved greatly. With a GOOD BMS, TBH I don't really have a problem with them any more, safety wise. User maintenance is nil, mostly just keep them clean and connections tight, visually inspect, and manually check case temperature and stuff once in a while. A proper BMS should alert you when something isn't right. Whether they are economically feasible for you is another question. They can be discharged quite deeply and suffer much less for it than the various lead acid types. Under reasonable operating conditions they last quite a long time, 10 years not being impossible at all. They are fairly light weight and so the energy density is high. All the cool kids have them.

However I feel that the biggest bang for the buck you can get is GC-2 golf cart batteries, if you can source them cheaply. Well maintained GC-2 batts should be good for about 7 years, if my experience with them in my e-boat means anything. They are true deep cycle, unlike most 8D batteries which are usually "marine" batteries, sort of a hybrid between deep cycle and start batteries. The conventional wisdom is never discharge FLA batteries below 50% SOC but I routinely went far deeper than that with mine. If the boat sits at the dock a lot, you need to equalize them occasionally. You need to check the water about weekly and top them up as needed. All the other stuff, like keeping the connections clean and tight and on the subject, remember since you will be running them in series for 12 volts nominal, you have more connections to fuss with. You would have to reconfigure your battery box. To replace two 8D you would typically use four GC-2 in series/parallel, for around 440 amp hours at 12 volts nominal, and this is a bit less than your twin 8D setup. If there is room, you might want three strings, i.e. six golf cart batteries, instead of just four. Do the math, crunch the numbers. The GC-2 are a very easy to handle case size and weight. I really like them, myself. Not everyone does. YMMV.

New technologies are cool. I like to watch other people spend their time and money on them. I do not care to be an early adopter, though. Not enough disposable income here, for that.

If you can't decide, best money says stick with what you already know about. I think your two best alternate choices are GC-2 FLA golf cart batteries, or possibly LiFePO4 if you don't mind the price tag, remembering of course that you get some of that back through longer battery life. Hopefully.

[sinnerman]

Originally Posted by senormechanico

The warm one probably has a shorted cell.
Disconnect it and I'll bet the voltage drops within a short time to around ten Plus.

Ditto

Cheers

[allendick]

Thanks. I have tested each battery separately and it seems they are now both below 50% capacity. Connections are fine. No shorted cells. Just weak.

I read the Lifeline document and may try equalizing, or as they call it, conditioning. I may have to isolate devices on the DC circuit, though to avoid damage. Haste makes waste.

I have had golf car batteries in the past and they are a good choice but it seems that ny all accounts that the new lithium batteries are better in many ways -- if the right ones are installed.

Will Prowse cuts some apart in videos and it seems that there is a wide range in quality.

I am not in a rush and will check the current batteries out further before making a move. Even with reduced capacity, they are adequate (barely).

I also have to consider what I can get reasonably easily and the cost here in La Paz.

I appreciate all the comments and see I have more homework to do.

Thanks.

[sinnerman]

Did you use a load tester on the battery.

These will actually load-stress the battery to see how it reacts underload.

You can buy them relatively cheap device on line. Or you can bring it to an auto store and they will do the same test for free...

My two cents

cheers