Can a Battery be Reverse Charged?

What?!!!!

I think explosions can happen.

If you did this and your battery is still okay, I'm guessing that your charger probably has a safety feature built in to prevent sending a charge to the negative terminal.

With a lead-acid battery it will reverse charge, but you may compromise the battery life and efficiency.

I know the two poles are different materials (lead anode and a lead-oxide cathode).

So, the chemical process is going to be slightly different and you may also overheat the battery solution is charged too fast. Exploding H2SO4 is very bad stuff.

Don't do it. If you did it once and got away with it, don't do it again.

"An unscheduled undesired thermal event."

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Yeah, that doesn't look scheduled or desirable.

How about: An unscheduled undesired thermal event, resulting in energetic disassembly of the battery.

Or IED.

You run the same high current situation if you connect a fully discharged battery to a fully charged battery.

It will not matter which pole is connected to which. The discharged battery will still be a very low resistance and a high current sink.

Agreed.

My very much simplified illustration counts on "The two batteries are identical, but one holds slightly higher charge." being true.

New Battery? Length of time it was used charged in the reverse state? If relatively new may be corrected if the battery is full discharge. Then brought back up to charge with the proper pole potential with a charger that you can control voltage and amperage. You may need to seek a battery service company to find such a charger. If not in service too long in reversed voltage state should not effect life too much.

Note if these is not an industrial battery time cost to reverse it not worth the cost of new a battery.

Because charging a lead acid battery in reverse is such a bad thing I don't really have any detailed information other than the following.

If you connect up a partially discharged lead acid battery to a charger in reverse accidentally and......

1) disconnect it almost immediately (and the charger still works), both the battery and charger will probably be unaffected.

2) leave it to charge for an extended period of time then permanent chemical and heat damage will be done to the battery, either killing it or greatly reducing its life (and likely capacity)

3) the battery charger is equipped with good protection circuitry it may not charge the battery at all, preventing damage to either of them. This is unlikely to happen with standard (cheap) lead acid battery chargers, although you may get away with it with more advanced Sealed lead acid multi stage charger.

All in all if the battery survives it will most likely be damaged, the extent of the damage can be found by performing a discharge test to see how much life is left (discharge time is a good indication of battery life), although care needs to be taken as a damaged battery cell due to reverse charging could result in unpleasant consequences.

Alternatively, just replace the battery if you accidentally reverse charge it for more than say a few minutes.

If the circuit has been protected correctly then the circuit protective device will operate, disconnecting the charger from the battery.

If there is no protection then fire/explosion/property damage/injury, or any combination of them, may ensue.

Then again we have someone who has invented a lead-acid battery reconditioning system that deliberately subjects them to reverse charging...

"...During use, two types of lead sulphate form on flat batteries, the first type is conductive and allows normal recharging, the second is hard lead sulphate that insulates and inhibits normal re-charging. If the battery is almost completely drained, reverse charging with adequate current control breaks down the hard sulphate and a few charge-discharge cycles can restore useful operation.
If controlled-current reverse charge is done long enough, the chemistry of the reactions will cause the polarity of the battery to also reverse as the lead compositions coating the plates reverses. If that's your question,I have no data on the resultant voltages, or the efficiency of such reversed-operation batteries, but they are technically possible if done correctly and currents controlled safely..."

Reverse charged, reverse polarity and it still works!

I have an flashlight with an S.L.A.B..

I've charged it with reverse polaity and the battery is still ok, it still holds the power and it performes quite good.

The reverse polarity charge was not atempted intentionally, it was an result of bad connecting the charger (the battery is included in the case of the flashlight and it connects by an common jack)