I think I killed it.

[A.Justice]

My 4runner has been up on jacks for about a month with some transmission problems, and I haven't charged the battery in that time.

It's a standard-FLA starter battery.

It reads 2 volts, and when I hook my bench power supply up to it it won't take more than a half amp. I connected the power supply to another load and it delivers just fine, so I know it's not up PSU issue. Connections are good enough as well.

I don't know much about flooded lead, are there any steps I can take to attempt to revive the battery before I buy a new one?

 

[sunshine_eggo]

Check that the plates are covered with electrolyte. If not, add just enough distilled water to cover them. Don't completely fill cells.

It's probably dead, but there's no harm in trying. Set your PSU to 13.8V and 6A and just let it sit there for about 24 hours. If it's not completely dead, it should slowly take more current, hit 13.8V and then taper like you would expect. If that works, full charge by going to 14.4V for the sooner of 4 hours or until the current drops to about 1-2A. Should be very nearly fully charged at that point.

If the battery gets hot at any point, let it rest until it cools and then check voltage. If it can't maintain 12.3V after a cool down or an overnight sit, it's probably not worth any additional effort.

 

[A.Justice]

Check that the plates are covered with electrolyte. If not, add just enough distilled water to cover them. Don't completely fill cells.

It's probably dead, but there's no harm in trying. Set your PSU to 13.8V and 6A and just let it sit there for about 24 hours. If it's not completely dead, it should slowly take more current, hit 13.8V and then taper like you would expect. If that works, full charge by going to 14.4V for the sooner of 4 hours or until the current drops to about 1-2A. Should be very nearly fully charged at that point.

If the battery gets hot at any point, let it rest until it cools and then check voltage. If it can't maintain 12.3V after a cool down or an overnight sit, it's probably not worth any additional effort.

Thank you.

I just checked the plates, they are all full, I don't see any sort of visible debris, and they appear clean.

Power supply is connected at 13.8 volts now.

 

[Zwy]

My 4runner has been up on jacks for about a month with some transmission problems, and I haven't charged the battery in that time.

It's a standard-FLA starter battery.

It reads 2 volts, and when I hook my bench power supply up to it it won't take more than a half amp. I connected the power supply to another load and it delivers just fine, so I know it's not up PSU issue. Connections are good enough as well.

Internal resistance is probably high, just leave the power supply on it. Set voltage around 14.5V, it won't matter until the battery gets close to full charge as the power supply will max out on amps.

I don't know much about flooded lead, are there any steps I can take to attempt to revive the battery before I buy a new one?

There are steps to take, requires time to remove sulfation. Once you get a full charge in it, load test it. If it fails, charge to full charge again, then you move on to equalization type of charging to remove sulfation.

The most important part thru all of this is to keep the plates covered with electrolyte.

 

[A.Justice]

It finally hit 13.8, I have it set on 14.4 now, with a 4-hour timer going. It was going at night so I wasn't able to see if the charge rate increased. Fingers crossed.

 

[efficientPV]

I've taken batteries with less than 10mv and charged them. It does take a long time and sulfation may not be fully reversed.

 

[Browneye]

Uhm....it's toast...now a trip to wallyfart.
If it went flat in a month it was toast anyway. Those things really need to be jerked out at no longer than five years anyway, regardless.

 

[sunshine_eggo]

Uhm....it's toast...now a trip to wallyfart.
If it went flat in a month it was toast anyway.

Not if it was connected to the car. I've frequently measured a parasitic draw of 15-40mA. That's almost 1Ah/day.

Those things really need to be jerked out at no longer than five years anyway, regardless.

Without regular maintenance charging and health checks, I agree.

 

[robby]

Sorry but...

 

[sunshine_eggo]

LOL... I will add that a battery that is allowed to go flat like that has experienced a notable reduction in anticipated service life.

 

[Browneye]

LOL... I will add that a battery that is allowed to go flat like that has experienced a notable reduction in anticipated service life.

This is what I'm getting at. It's just not worth futzing around with. Replace it.

At one time, when I had all my motorbikes and cars and boats and stuff, I had 15 starting batteries. If you didn't keep them fully charged they just go to $hit.
Even new vehicles and motorized recreational craft sitting on a dealer showroom - if they let them drop down the battery never gets past a year or two. Lead acid batteries, especially starting batteries, just don't last unless they're trickled and kept full. They just won't hold a charge.

I've had batteries that measured 12.5V on a DMM and as soon as you put a load on them they would drop out to nothing. Those are shorted plates. I took the starter out of a yamaha dirtbike three times, even disassembled it thinking it was bad. Nope...just the $40 battery. The newer ones don't even have a kickstarter anymore so you're stuck.

 

[RCinFLA]

All it takes is a dome light to be left on that about of time to totally deplete battery.

Just like leaving your head lights on all day, draining a lead acid battery that low will never be the same again. Just like a deep cut wound, it will leave a scare. I would not trust its long-term service performance.

 

[A.Justice]

It's dead. The good news is I think it might still be under warranty, if not, it might be a good time to try to build an LTO bank.