How can a battery change it's polarity!!!!!!

[Furgus]

I managed to run the batteries flat in my 24v LR, I disconected them from each other & charged the first one no probs, then I came to charge the second one and it wasn't happening........ After some confusion & head scratching I got the volt metre out & check to see how much it was down, imagine my surprise when it read -8.46!!!!!!!!!!! So i swapped the tester terminals over (-ve on meter to +ve on battery etc) and yes it read +8.46.
Yes I did double check on the other battery and the metre is connected up right ........ WTF is going on????????

[DaveM]

If a battery is fully discharged and continues to have a load, for example leaving the headlights on, it is possible for one or more cells to reverse polarity.
When the battery has been recharged with reversed polarity the polarity can change.
To change polarity, fully discharge the battery and recharge it with the correct polarity.

[Aaron]

or you could run it as a positive earth vehicle like a morris minor after all it is english