At the office (elderly living building) we have a large battery backup system with 12
110 amp-hour AGM batteries. Seems that soon after they were replaced 2 years ago the
charging circuit popped a fuse so they had been periodically tested and used with
no charging. After yelling that testing involves looking at the volt meter mounted
on the front and after writing a check for $2,800 to replace them I offered to take
them home and mess with them. Worst case I'm out a few amps of electricity and a
sore back.
Had to walk past the beer fridge in the unloading process. Made it through the first
10 before the beer won. Each 12 volt battery measured less than 1 volt. Didn't know
you could get a battery that low...
Put a trickle charger and de-sulfinator on 4 in parallel in the garage and threw a
20 watt solar panel in the back of the car to charge the 2 in there. End of the
next day it was hot in the car, and the batteries were in full sun. Heat is bad for
batteries so I figured I had killed dead batteries. Got home and pulled out the volt
meter. Garage batteries charging for 24 hours were still below a volt. 2 Car
batteries charging from panel and well heated were at 5 volts. Hum...
Shortening up a long story - 3 weeks later each battery has spent a day or 3 in the
hot sun with a trickle charger and desulfinator. I unscrewed the tops to relieve
pressure and added a little water, just enough so that the material between the
plates looked damp, but no standing water. 10 of the 12 show resting voltage
(overnight with no charging) of between 12.85 and 12.91 volts. 2 won't get above 12.
I've had the 10 wired into my system for a week now and they are working great!
I wouldn't try this with good batteries but if you've got some due to be hauled to
the recycler it's worth a try. Note: I'm talking leave them out in the sun heat,
not pre-heat oven to 350 heat!
-Henry