I have a 100-ish amp-hour AGM marine/RV battery in my trailer. I charge it with solar so that I don't have to worry about it, but over the holidays it was sitting for 2 weeks with the cameras turned on and apparently they suck out more power than the solar can put in (at least in December when it's cloudy and raining). Went out there yesterday and it was reading like 4 volts.
My smart charger won't charge it -- reports "F01", meaning it thinks there's a shorted cell. This is pretty typical for AGM batteries that are heavily drained, and the fix I've used in the past is to hook up a second 12v battery in parallel so that it presents enough of a load to fool the charger. Do that for a couple hours and it puts enough charge into the battery to get it working again. I did that this afternoon and it's up to 6 volts, but when I go back to charging it by itself I still get "F01".
The solar charger seemingly wants nothing to do with it.
Any thoughts? I have a 1.5 amp trickle charger I could stick on it. Or is it just dead and I should go buy another one?
Charge a lead acid in conjunction with the agm. Once it's all charging, disconnect the lead acid and continue to charge the agm until done.
You can chuck on a dumb 12V power supply also, or just leave the parallel lead acid connected longer. I've had no problem bringing back batteries over a decade old like this, but sometimes it can take a week.
Ranger50 said:
Charge a lead acid in conjunction with the agm. Once it's all charging, disconnect the lead acid and continue to charge the agm until done.
Yeah, that's what I've been trying and it hasn't worked so far (well, it brought it from 4 volts to 6). Perhaps the problem is that the other battery is mostly charged already? It's a little motorcycle battery, also AGM. I'm not actually sure I have any regular flooded lead-acids unless I want to take one of the batteries out of the truck.
bbbbRASS said:
You can chuck on a dumb 12V power supply also, or just leave the parallel lead acid connected longer. I've had no problem bringing back batteries over a decade old like this, but sometimes it can take a week.
You can let the smoke out of an AGM battery (literally) unless you use an appropriate charger.
I'd pair it to a fully charged battery and just let it sit like that, no charger.
It does sound like the battery may be done. It's worth a try to charge it, but I would be ready to accept that it won't.
Pete. (l33t FS) said:
You can let the smoke out of an AGM battery (literally) unless you use an appropriate charger.
I'd pair it to a fully charged battery and just let it sit like that, no charger.
Yeah, last night I alternated between charging in parallel, just letting it sit paired to the charged motorcycle battery, and trying to charge singly. It's up to 10 volts after that, so hopefully another few iterations of that will bring it back.
I don't have a dumb charger and I'm not even sure you can buy them any more. The battery is also buried deep within the cabinets in my trailer, so I certainly don't want to risk setting it on fire and pulling it out is enough of a PITA that I'd rather not do that if I don't have to either. :)
If you're up to 10 volts, it may come back. I've resurrected an old AGM battery a few times by using the second battery in parallel method. After getting the AGM battery charge up enough for my charger to recognize it, I removed the second battery. With the charger hooked up again to the AGM battery alone, I think I recall that it still took at least overnight before it was fully charged.
Update: I spent 3 days going out to the trailer every hour or two to check on it, swapping it between charging in parallel and just letting the good motorcycle battery charge the dead big one, it hit 11.5 volts this afternoon and that was enough for the charger to be happy charging it normally. It's not quite all the way back to full charge yet (I don't like leaving the charger on it unattended overnight), but it looks like it's coming back.
