Battery Charging

[amishman]

I have a battery charger I purchased from a local parts store a long time back. I don't use it much other than once or twice to trickle charge a battery. Mine has a 6amp 12 volt setting for a more complete charge.

Is there a minimum voltage the old battery needs to be at in order for it to charge and be usable again? I just want to use the battery on a engine test basis when seeing if an old VW engine runs outside the car. Not for use in a car since it is old.

Anyway, the battery is at 9.5 volts now. Is that chargeable or beyond life now? I have two maybe 6 to 8 year-old batteries that I have had in my garage. They sat for a year or so and 9.5 volts is what the first one tested at before I stuck it on the charger. I will let it charge overnight.

Just curious what the chances are it will go 12v again.

tj

[vwlover77]

Batteries are strange and mysterious. Seems like they'll recharge when you'd never believe they would, and die a sudden death when you'd least expect it.

I believe the only way you'll know for sure it to try to charge it! Check the water level if you can. If it's at 9.5V with low cells, that could be a problem, or not, depending on how long it has been sitting around. If it sat for a year and is still maintaining 9.5V, I'd guess it's a good battery.

[glasseye]

Colin will no doubt chime in here, but I'm of the understanding that the only reeeely valid test of a battery is its voltage under load. Open-circuit voltages are inconclusive, lying weasels.

[Amskeptic]

9.5 after a thorough charge is junk.
What is a "thorough charge'?
Glad you asked.
It is 24 hours at 2 amps. Caps loose, electolyte level topped off.
Colin

[amishman]

9.5 after a thorough charge is junk.
What is a "thorough charge'?
Glad you asked.
It is 24 hours at 2 amps. Caps loose, electolyte level topped off.
Colin

Am I wrong for doing 6amp overnight then? What is the difference between doing 2amp and 6 amp.

I thought 2amp was trickle and 6amp was doing a more full charge.

tj

[Amskeptic]

Am I wrong for doing 6amp overnight then?
I thought 2amp was trickle and 6amp was doing a more full charge.

No, a 6A overnight is roughly equivalent to a 24 hour 2A trickle charge. The battery prefers the trickle charge. There is a time component to fully dissolving the lead sulfate back into the electrolyte. 6A is only faster and hotter. 10A is hotter still. Quick Start Turbo Boost is hotter still, damagingly so.
Colin

[amishman]

So, I did a 12v 6 amp over night, about 14 hours or so, and it went from 9.5v to 12.55v.

Maybe it has hope.

Do I just wait now for a week and see if she still holds 12+ v sitting that long?

Is there some easy test I can do to confirm it is usable?

By the way, what should a 12v battery maintain after it sits for a week or two without being used? Is it anything over 12v is fine. My guess is the 12.55 I have now will decrease over sitting time but wonder what the minimum it should maintain sitting on a shelf for months.

I guess I can just plug it in and juice it up every month or so.

tj

[Amskeptic]

Is there some easy test I can do to confirm it is usable?

By the way, what should a 12v battery maintain after it sits for a week or two without being used?

Stick it in the trunk in a box and take it to AutoZone for a free load test.
Make sure it is fully charged.

After a week of sitting out of the car, you should see no deterioration in charge whatsoever. I think the static surface charge is normally 12.7+
Colin

[amishman]

Is there some easy test I can do to confirm it is useable?

By the way, what should a 12v battery maintain after it sits for a week or two without being used?

Stick it in the trunk in a box and take it to AutoZone for a free load test.
Make sure it is fully charged.

After a week of sitting out of the car, you should see no deterioration in charge whatsoever. I think the static surface charge is normally 12.7+
Colin

Good idea on AutoZone.

After a few hours being disconnected from my battery charger it went from 12.55 to 12.20 or something like that. I know my New Beetle battery that is fairly new fluctuates from 12.6 right after driving it to 12.2 after a day or two not driving it. My guess they drop a tad but stay above 12.

I will try that AutoZone idea.

Thanks!

tj