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I’ve seen people ask how to discharge a lead-acid battery, which is easy enough.

I have a lead-acid battery that I must have connected to my on-board boat charger backwards. It must have been very dead, because it reversed the polarity. I know to reverse it back, I’ll need to discharge the battery pretty completely.

My question is how much damage is this going to do to the battery? Is there any other way to reverse this polarity without discharging completely?

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  • \$\begingroup\$ As far as I'm aware, the best thing to do is throw out the battery and get a new one. The one you have is probably never going to work well again. \$\endgroup\$
    – Hearth
    Sep 15, 2019 at 13:27
  • \$\begingroup\$ It’s practically a brand new battery or I would toss it. Since it’s new I think it’s worth a try to drain it and try to get it to reverse back to the proper polarity. It doesn’t have to work like a new one. If it last me the rest of the season it’ll be worth a little bit of my time. Then I’ll have till spring to get a new battery, or three. That’s what it takes to run my troll motor and I’ll probably just get three new ones for the start of next season. \$\endgroup\$
    – Jerry Love
    Sep 15, 2019 at 16:16
  • \$\begingroup\$ My college once did that to revive a dead (sulfated) battery in his youth when money was tight. Gave him one more season out of it. Highly inadvisable though due to dangers involved and that the battery is asymmetrical inside so it will struggle at the very least to be reversed. \$\endgroup\$
    – winny
    Sep 15, 2019 at 19:38

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After reading up on an article on this matter, it seems that the only way to fix this issue is to completely discharge the battery. (article) Now since lead-acids do not want to discharge completely (80% is the rated limit before damage is done to the battery), there is no "safe" way to get rid of the reverse polarity effect on the battery.

One thing you could do, but this would ultimately lead to the destruction of the battery plates inside, is to use the battery in reverse. The battery plates are not meant to be charged in reverse, so continuous cycles of charging and discharging will destroy them, but you could maybe get a few cycles out of it.

Overall, the best course of action is to buy a new battery.

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