Hungary Bill
Hungary Bill Dork
11/5/13 1:45 p.m.

I used this trick on an Optima battery when I found a pile of them in a bunker on base.

The nitty gritty:

  • The trickle charger was on this dead battery all night, but the needle didn't even move.

The fix:

  • Hook the battery charger up to a good battery and start the charging

  • Use a set of jumper cables to hook the charging battery (your good battery) in parallel with the bad battery while it is charging

  • Let 'er charge

After a couple of hours your dead battery should have enough juice to give the charger it's reference voltage. You should be able to remove the good battery from the equation and let the charger do it's job from there. So far the Optima red Top I used this trick on has been working solid for three years (first installed in my Lada, now my Impala). Not bad for a free battery.

GameboyRMH MegaDork
11/5/13 1:50 p.m.

You say "in series" but your diagram shows a parallel connection.

Kenny_McCormic UltraDork
11/5/13 1:53 p.m.

The cheap "dumb" roll around chargers/starter boxes don't have that problem.

4cylndrfury MegaDork
11/5/13 1:54 p.m.

Damn...and I just passed on 2 dead yellow tops...Thanks for posting this

Hungary Bill
Hungary Bill Dork
11/5/13 2:07 p.m.
GameboyRMH wrote: You say "in series" but your diagram shows a parallel connection.


(I always get "series" confused with "parallel")

Basil Exposition
Basil Exposition HalfDork
11/5/13 8:20 p.m.

BTW, if you go to Optima's website this what they tell you to do to revive one of their batteries.

cdowd Reader
11/7/13 1:17 p.m.

good to know. I have a few old batteries for old cars that i could try this with.

Dusterbd13 Dork
11/11/13 5:54 p.m.

thanks. can I use a lawnmower battery as one of them? I have a good one....

battery in the duster wont even THINK about taking a charge from my charger, so this trick is very important to me at this moment. why? because im flat broke.

Hungary Bill
Hungary Bill Dork
11/12/13 9:21 a.m.

I'd say for sure that you can if it's 12v. I'd have my reserves about hooking up a 6v and a 12v together and hooking them to a charger...

Do you have two 6v batteries you can connect in series to make a 12-volter? or can you "borrow" a battery from a neighbor/wife/girlfriend for an hour?

pres589 SuperDork
11/12/13 9:48 a.m.

This is all just to get around a low-voltage cut-off used on most trickle and modern smaller amperage battery chargers, right? I mean, you're still just wedging watts into an old battery with a reduced capacity, and not actually reconditioning it somehow, yes?

And yeah, advantage old chargers that don't have such things, but you have to baby-sit them.

Hungary Bill
Hungary Bill Dork
11/12/13 1:36 p.m.

That's correct. You're just giving the charger a "reference voltage".

Dusterbd13 Dork
11/13/13 8:37 a.m.

ok. cool. thanks, guys. ill be popping the battery out of my mower tonight and giving this a shot. heres to hoping that the duster will take a charge.

Hungary Bill
Hungary Bill Dork
11/14/13 9:04 a.m.

May the force be with you

Andrei Wright
Andrei Wright New Reader
5/17/14 4:40 a.m.

Tried this one before and that is so cool! Do try it guys! A lot of people might think old battery is already a garbage but this trick will prove you wrong.

Evan New Reader
6/6/14 7:34 p.m.

Here's the writeup from the Optima site.

Recovery Option #2: The DIY Solution

This is a recovery method for the do-it-yourselfer using the equipment you've got in the garage. With this option, you're going to trick your traditional charger into charging the deeply discharged AGM battery.

Here's what you need:

Battery charger (under 15-amps) Jumper cables A good battery, preferably above 12.2 volts. (It can be an AGM or flooded battery, it doesn't matter.) The seemingly dead, deeply discharged AGM battery A voltage meter A watch or timer

Now, here's what you do:

  1. Hook up the good battery and deeply discharged AGM battery in parallel – positive to positive and negative to negative. Do not have the charger connected to the battery or turned on at this stage.

  2. Now, hook up the good battery to the charger. Turn on the charger. The charger will "see" the voltage of the good battery (hooked up in parallel), and start providing a charge.

  3. After the batteries have been hooked up for about an hour, check to see if the AGM battery is slightly warm or hot to the touch. Batteries naturally become warm during charging, but excessive heat may be an indication that there really is something wrong with the battery. Discontinue charging immediately if the battery is hot to the touch. Also discontinue the process if you hear the battery "gassing" — a hissing sound coming from the safety valves. If it's hot or gassing, STOP CHARGING IMMEDIATELY!

  4. With your voltage meter, check back often to see if the AGM battery has charged to 10.5 volts or above, this generally takes less than two hours with a 10-amp charger. If it has, disconnect the charger from the wall outlet and remove the good battery from the charger. Now, connect only the deeply discharged AGM battery to the charger. Turn on the charger and continue until the AGM battery reaches a full charge, or until the automatic charger completes the charge process. In most cases, the AGM battery will be recovered.

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