Reverse polarity on AAA non-rechargable

[erik.calco]

I took 4 AAAs out of a remote control and tested them with my multimeter. One of them reads a negative charge (-0.5V) in normal direction, and a positive charge in reverse direction! Another cell correctly reads 0.7V in normal direction.

How can a cell develop a reverse polarity?

Just a curious scientific question. In case you think it is human error, I do this all the time for years, measuring AA and AAAs hundreds of times, but usually for my rechargeable cells before and after charging. Plus, I have the correct cell next to that that was in the same series in the remote that reads correctly.

 

[BiduleOhm]

When you have multiple cells in series the weakest one will be discharged before the other ones. If you keep pulling current then the other cells will try to charge the discharged cell backwards.

That's why it's always written in the manuals to not mix battery types, or new and used batteries.

 

[erik.calco]

That makes sense.

In a related story, I pulled two batteries that were in series from my UPS. One had 7V, another 0V. I'm trying to revive the 7V one. Got it to 11V yesterday on an AC charger. You can revive some really dead ones by putting in parallel with a good cell, but risk damaging the good cell and have to really monitor that. So, undecided if I'll try to revive some of my really dead batteries.