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The next thing to try is to grab another battery and hook it up in parallel. You can also use something like a 12volt light bulb (you need a LOAD to put on the charger so it will provide output).
THe internal resistance of the Optima is too high, in its current (NPI) state of charge.

Make sense?

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I have a red top Optima that I can't get to charge. My regular battery charger will try to charge it, but as soon as I remove it, I read 4.5 volts at the terminals. I also tried a battery tender specifically for AGM batteries, and it won't get it over 5 volts. Is there a way to revive them, or is it junk?

Dennis

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I bought at a yard sale a 2-year-old red top Optima (clean, still had the "4/10" date stickers on it) for $30 that was supposed to have been removed from the car last week. I think they neglected to tell me the car had been sitting for a year before that... got it home and it had 0.1 volt Figured it was toast and I had a $7 core

I hooked it to an old-fashioned 8-amp charger (none of that float, auto shutoff, etc.) and at first it would not take any current. After about 20 minutes it began to draw a couple of amps and I left it on for several hours and it gradually climbed to 5 amps. Shut it off overnight and went to bed.

Next morning had 11 volts, 9.5 on my 100-amp load tester... better. Then I looked on the manufacturer's website and it says it's ok to blast it with a high charge rate to break up the sulfation, as long as the battery temp did not exceed 125F. So I hit it with 40 amps from the wheel-type charger for an hour until it was warm, discharged it all day through a one-ohm power resistor, then fast-charged again until it reached 15 volts (while charging), and backed off to about 20 amps until it was charging at 14.5 volts. (I could have gone to 15.5 volts, no current limit, without hurting it, again as long as it stayed under 125F).

(The reason for not fast-charging it at first, before cycling once, is that I could not be sure all six cells were equalized, and if one were much weaker it could result in overcharging the others...)

Now it's just in the green on the load-tester meter and has over 12 volts just sitting there Probably not as good as if it hadn't been allowed to sit totally flat, since it's impossible to break up all the sulfate, but for $30 instead of $189...

-Charles
ps as someone else (and the mfr.) pointed out, if your automatic charger won't kick in because it's too low, put another battery in parallel to get it going.

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Unfortunately I think you're probably right... but how much current was it drawing while on the regular charger? and what was the terminal voltage while charging?

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