How to Charge a Very Dead 12V Battery

[Provience]

welp, in a bonehead move I drained the battery on my truck the other day. Didn't disconnect the courtesy light switch after taking apart the door, and left the inside lights on for about 3 days before I went back out that. battery was showing just over 4v...oof.

wouldn't register on the charger, so i hooked it up with jumper cables to another battery I had, let it sit like that for an hour or so to help bring up some charge/balance the two batteries without running a bunch of volts to it. This battery is only a couple months old, so odds of success are good.

After the voltage quit dropping fast, I hooked the charger up to the 'good' battery, mostly out of convenience. Doubling the capacity makes it seem like the dead battery isn't such a big deal

Now there is enough for the charger to see, it thinks the whole bank is running about 50% capacity and can do some work

and with everything charging at 14.36 volts. there are both lead acid batteries, so they can handle a fair bit of abuse. 14 volts isn't much at all, checked it periodically and neither was getting warm, cables never got warm. Let it run for a couple hours.

After a couple hours, unhooked the spare battery and put the charger alone with the 'dead' one. had enough volts at this point to be recognized, let it run for a few more hours.

Unhooked everything, after an hour it was still showing over 12 volts

truck ran like absolute shit at first, shut it off, started it again and it smoothed itself out.

small tech is still tech, so might as well post it. With an older battery that is very dead, it may need to be opened up and cleaned/refilled with acid before being able to hold a charge. this is free and easy, worth trying for very low batteries.

[Scott Cee AKA 2drx4]

Aww, you missed the chance to charge it backwards. Just do what you did but reverse the leads on it. Bingo, instant reverse post battery that's not good for fuckall.

[Provience]

hadn't considered that.

wife was convinced i was going to burn the truck down, so that's why i had to keep checking it. prove to her it wasn't getting hot

[Johnny5]

Around here if a battery goes dead over night chances are its gonna freeze and buldge. Lol not much ya can do with a round battery

[Provience]

Around here if a battery goes dead over night chances are its gonna freeze and buldge. Lol not much ya can do with a round battery

cut it open and rebuild it anybody sell new cases up there?

[pointsnorth]

I’ve used this method a lot especially super dead optimas


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[pointsnorth]

Around here if a battery goes dead over night chances are its gonna freeze and buldge. Lol not much ya can do with a round battery

cut it open and rebuild it anybody sell new cases up there?

the bulging leads to the plates in the lead acid battery distorting and touching the battery is generally scrap then

[Provience]

Around here if a battery goes dead over night chances are its gonna freeze and buldge. Lol not much ya can do with a round battery

cut it open and rebuild it anybody sell new cases up there?

the bulging leads to the plates in the lead acid battery distorting and touching the battery is generally scrap then

ah damn, i haven't had the joy of dealing with that sort of fun cold yet. are the AGM's less susceptible to freeze ?

[Scott Cee AKA 2drx4]

The AGMs will freeze solid and come back to life. I don't think it's great for them, but it is part of the reason I use them in my fleet of obsolete vehicles that sit a lot.

I used to kill a couple regular flooded cell lead acids every year before I switched. If you don't realise one has froze and split, and you leave it until it warms up, they spill acid everywhere and wreck stuff even more.

[Provience]

awesome. i quit buying AGM's a decade, decade and a half ago maybe, after i had a couple issues in a row with some optimas. they've probably got everything fixed by now, with whatever they were doing, but being cheap hasn't been bad down here in the land of mild temperatures

[Mr.gutsy]

I was expecting the old epson salt trick. Guys will hit dead batteries with a 40amp charger for a little bit to shock the plates then throw a trickle on them at work. Ive never really bothered trying. AVE has a pretty good video on some of the theory if anyone follows him.

[Provience]

what's the epson salt trick? i wish i had a 40A charger, but the rockcrawler keeps won't hardly let me walk past it

[Scott Cee AKA 2drx4]

If you have access to the cells you can add Epsom salts to the acid to "rejuvenate" them. It works, sorta, I mean you're fucking an already fucked battery so it's not that big of deal at that point.

[Provience]

right on, haven't ever tried that before

[Johnny5]

Ya you can hit some of them sulphated batteries with “start” mode for like 20 min to force the sulpher build up off the plates. If ya accidentally leave it too long theres a nifty feature that the battery has where it releases a smell to remind you lol