Battery polarity reversal

[Kevin1908]

I have some head torches that wouldn't work so decided to get to the bottom as the problem didn't solve the issue. Cleaned up a bit of corrosion on the contacts but no sign of the batteries leaking. Decided to check the voltage of the non rechargeable AAA batteries. All fine except one. It has a healthy voltage but the wrong way round. I gather a rechargeable battery can get reverse polarity but how on Earth can a non rechargeable battery be the opposite way round? Still can't get one torch to work, could the reverse polarity battery have damaged it or just faulty for another reason such as faulty LED.