Help w/AMG deep cycle marine battery

[Cheetah]

I've got two of these monsters bought exclusively for use on playa (swamp cooler, lights, etc.) and despite what I thought were good maintenance habits (and only one having been used once, the other never used) both are messed up (the tester says to replace). I've tried draining them (not too far, around 70) which seems to help the SOH and resistance numbers, but when I charge them those numbers immediately nosedive (like single digit SOH and resistance in the 50s). Voltage seems normal range.

Wtf is going on? Do I really need to buy a new battery?

[Popeye]

Sounds like you need to replace it and keep it charged in the off season.
An AGM battery and a lead acid are damaged when the charge goes below about 50%.
A lithium can be discharged to about 10% before damage. For long storage leave it charged to about 75-80%.

[Cheetah]

I actually did monitor both (never dipped below 50%) and kept them charged off season. And yet they're both f---ed and I don't understand why. I did consider that they don't like the BRC heat, but then wouldn't everyone have this issue?

Question: since I'll have solar setup to keep them charged on playa, will they serve their purpose? Or is there a high chance they'll both die on me?

Buying a new one seems the easy answer, but won't I just end up with a third useless battery??

[Jackass]

What tester are you using?

If the voltage is fine then run it, you should be able to test run them with your loads now and see how they hold up.

I have a problem with some of these testers and automatic battery chargers that tell you the battery is junk, they lie, a lot.

[Popeye]

The very best way to test a batter is with a load. I use this tester.

[Token]

I've got two of these monsters bought exclusively for use on playa (swamp cooler, lights, etc.) and despite what I thought were good maintenance habits (and only one having been used once, the other never used) both are messed up (the tester says to replace). I've tried draining them (not too far, around 70) which seems to help the SOH and resistance numbers, but when I charge them those numbers immediately nosedive (like single digit SOH and resistance in the 50s). Voltage seems normal range.

Wtf is going on? Do I really need to buy a new battery?

I do got to say, problem is likely in the keyboard-chair interface.

You pretty much did everything wrong.

AGM batteries are sealed and have precise valves to allow water escape. “Draining” anything on an AGM - bad.

These batteries have a Glass Mat between the plates that hold the electrolyte (hence the name Absorbent Glass Mat) and are designed as sealed batteries with specific off-gassing valves.

Regardless of how you got to thinking they were bad, now they ARE bad.

BTW, easy way to kill any lead acid battery - put it on the ground on concrete in a damp garage or basement. Even trickle chargers on them if on the ground like that - deadski with enough time.

Bite the bullet and chalk it up to the school of hard knocks.

[Cheetah]

I can't post a pic of my tester (and I don't see an image above), it's a KONNWEI KW218 6V 12V Car Battery Tester 100-2000 CCA. Not the cheapest nor the most expensive. I do take the results with a grain of salt and rely more on the numbers.

I wish I understood what it is that I did wrong so at the very least I could avoid making the same mistakes with a new battery. I know it's not good to completely drain (I haven't, lowest it's ever been is 50%) nor to overcharge. Why are these things so fragile??

[Token]

I can't post a pic of my tester (and I don't see an image above), it's a KONNWEI KW218 6V 12V Car Battery Tester 100-2000 CCA. Not the cheapest nor the most expensive. I do take the results with a grain of salt and rely more on the numbers.

I wish I understood what it is that I did wrong so at the very least I could avoid making the same mistakes with a new battery. I know it's not good to completely drain (I haven't, lowest it's ever been is 50%) nor to overcharge. Why are these things so fragile??

Deep breath inhale …

AGM batteries have much lower internal resistance (thinner lead plates cuz the glass mat provides structural support for the fragile lead, more electrolyte capacity). Because of that they need a compatible charger that runs higher current than for flooded lead-acid batteries, but also lower voltage.

If you didn’t use an AGM compatible charger or controller (if this was solar) or forgot to set it to AGM mode - that can quickly overheat the battery and pop the pressure valves out to vent the gasses. If the battery stays vented, over time it will evaporate and cause oxidation of the plates - thus becoming broken.

AGM batteries must remain sealed or they deteriorate over time - oxidation. Most common cause : using a regular flooded lead-acid charger or not setting to AGM on a compatible unit.

So, the big error is opening the sealed battery and draining any fluids out of it. Even if the battery could have been recovered from say a sulfating problem with the right kind of pulse charger, now that fluids were drained out of the glass mats - no way to get them back in.

Another thing that went away once you broke the battery seal - any warranty. Many batteries have 3 or 5 year warranties. Most stores would just swap them out.

I literally just swapped out two dead Duralast Gold batteries from my diesel pickup that was sitting over a year, for free. Had 5 months left on the 3-year warranty.

Check the labels on the batteries to see if there is hope of a replacement, otherwise you need new batteries.

[Cheetah]

LOVE the detail of this post, so informative.

Just to be clear, I never opened these batteries. Wouldn't even know how.

And the charger is AGM compatible.

[Token]

Sorry, thought you said you drained them in the original post - yep, still there. How did you drain them or did you mean discharged them?

[Cheetah]

Discharged? Sorry a newbie so not versed in the lingo.

All I meant is that I connected devices to the batteries via an inverter. Which seems to improve their health.

At the burn, is it bad to leave the battery connected to a solar panel 24/7?

[M F Bonz]

I’m sorry if you don’t know what the word “discharge” means.
It’s unlikely any additional information exist that’s gonna help your situation. Thank you for playing.

Smiles ~

[Token]

At the burn, is it bad to leave the battery connected to a solar panel 24/7?

If you have a solar charge controller that supports AGM batteries - yes. Keep it hooked up.

Where we at? Couple-few days before the drive to the burn?

You got two questions to answer:

1 - Is what you got right now good enough for your burn? Yes or No answer.

2 - Is the hundreds of pounds of what you got critical for your burn? Yes or No answer.

After that it’s all good.

[Captain Goddammit]

BTW, easy way to kill any lead acid battery - put it on the ground on concrete in a damp garage or basement. Even trickle chargers on them if on the ground like that - deadski with enough time.

All great info as usual… but this part is a very common myth. The same battery that goes dead on a concrete floor also dies on any other floor.

[Popeye]

True Captain, but the battery will go dead faster on concrete than on most other things.
Batteries work by a chemical reaction, the concrete floor, especially damp, works as a heat sink cooling the battery and slowing the chemical reaction and dropping the voltage. When charge reaches roughly 50% or below the battery is pretty much worthless and won't take a charge any more.
Setting the battery on a board (as I was taught many years ago) slows heat loss and keeps the reaction going.
The same reason that a lead acid battery might die over the winter.

Welcome back Captain!

BTW, easy way to kill any lead acid battery - put it on the ground on concrete in a damp garage or basement. Even trickle chargers on them if on the ground like that - deadski with enough time.

All great info as usual… but this part is a very common myth. The same battery that goes dead on a concrete floor also dies on any other floor.

[Token]

BTW, easy way to kill any lead acid battery - put it on the ground on concrete in a damp garage or basement. Even trickle chargers on them if on the ground like that - deadski with enough time.

All great info as usual… but this part is a very common myth. The same battery that goes dead on a concrete floor also dies on any other floor.

Shhhh , don’t go confusing folks with myths.

That was solved long ago when we switched to HDPE casing, but now I gotta explain HDPE …

[Captain Goddammit]

I mean, I put up a new shop and did radiant heat in the concrete floor, so maybe my results may vary…

Hey everyone… I’ve been gone a long time… l started going to Hawaii instead…
I think it’s time to return to the playa!

[unjonharley]

I mean, I put up a new shop and did radiant heat in the concrete floor, so maybe my results may vary…

Hey everyone… I’ve been gone a long time… l started going to Hawaii instead…
I think it’s time to return to the playa!
[/quote

He's bringing that ugly boat too.