Battery with reverse polarity.

Are they mismatched ?

They say don't charge alkalines but that doesn't mean you can't.

Your topic here brought up a blast from the past. If a car had a starter mo tor with fieeld windings, and the radio was tubes which meant a vibrator, i t COULD concievably run on reverse polarity. And the batteris of the time d idn't care either.

You had to polarize the generator. Otherwise it oculd go either way, like a diesel engine starting backwards. It will run but won't have oil pressure. But on reverse polarity, there seemed like to be almost no problem. Of cou rse you would find out if you needed a jump start. but of course back then you just stick your foot out the door and get it rolling and drop the clutc h and start it that way.

Of course the battery had to have SOME chaerge left...

But anyway, what you describe is like the reason batteries now have more th an two terminals. Taps to make sure of balance, temp sensors and whatever o ther s*it they can come up with.

I know there's an issue with NiCd and NiMH batteries that if they've got a weak cell, when they're sucked dry that weak cell can get charged in reverse.

I have no clue what the chemistry of the reversed cell is, either in NiCd or alkaline.

Google "reversed cell"?

The battery that runs out of chemistry first is back-biased by the remaining ones.

If one cell is weak or flat, the others try to charge it in reverse via the load so it ends up with reverse voltage at the terminals. This can happen with any chemistry, including rechargeable types.

Also, if one cell in a string is installed in reverse the others try to charge it via the load. Makers of Alkaline cells warns against this as charging them can make the cell explode.

... Phil

Seen it with Duracells, I purchased 4 to run the CMOS/clock in an Amstrad PC-1512 (said PC has battery box for 4xAA in the top of the case) 6 months in one of them was -0.6V and the PC was alerting "CMOS battery low". I switched to Energisers.

This is correct. This is the main reason to never mix and match old and new batteries.

Worst case the dead ones start to leak.