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6 Volt Battery Charging?

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Great Horned Owl:
I just bought two 6 volt, 232 Ah, golf cart batteries. Initially, one of them was fairly well charged (6.38 V), while the other was not (6.04 V).

Since they are charging in series, the same current will flow into both of them. The one that started lower will never catch up, and will never get fully charged.

For reasons that I do not completely understand, the voltage difference between the two increased after several hours on the charger. At one point, I measured 6.59 V and 7.18 V. BTW, the manufacturer suggests bulk mode charging up to 7.75 V

I took took them off of the charger and hooked a 15 ohm load across the one with higher voltage until they were approximately the same. Then, I removed the load and connected the batteries in parallel to make sure that they were precisely the same. Next, I'll put them back on the charger in series.

Will this kind of imbalance keep happening? If so, is there a simpler solution, or am I worrying about nothing?

Joel

Gary RV Roamer:
The two will even out because the more charged battery will act as a charger and send current to the lower charged one. That's assuming the lower one is capable of reaching a 100% charge level. If not, the higher voltage one will continually fight to try to bring it up to equal, but will fail.

Great Horned Owl:

--- Quote from: Gary RV Roamer on June 30, 2012, 11:24:01 AM ---The two will even out because the more charged battery will act as a charger and send current to the lower charged one. That's assuming the lower one is capable of reaching a 100% charge level. If not, the higher voltage one will continually fight to try to bring it up to equal, but will fail.

--- End quote ---

Gary, I can see that happening while charging 12V batteries in parallel, but charging in series, current will always flow away from the positive terminal of the charger. In order for the higher one to send current to the lower one, current would have to flow in the opposite direction. That just does not seem possible.

Joel

Alfa38User:
You're letting complicated theories get in they way of facts. No two batteries are identical. Have them each load tested at any battery supplier. If one doesn't cut it, change it. In fact, they should be changed out in pairs but.... $$ count too.

Great Horned Owl:
It turns out to have been a non-problem.

I put them back on the charger for another 4 hours to equalize them, and they settled at a constant 7.21V and 7.51V. This was a lot closer.

After sitting overnight without being on the charger, they are now both reading 6.38V. Problem gone. The equalizing did the trick.

Joel

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