Electronic – Why do alkaline batteries seem to leak (corrode) more frequently when installed in a device

alkalinebatteries

I know that dead batteries can leak and the alkaline ones are specially corrosive.

Alkaline batteries self discharge even when not installed in any device.

I've already opened a four battery pack with one battery leaking, but this situation is by far more uncommon than finding leaking batteries in forgotten devices.

Nowadays some appliances have standby power that possibly in a long time can drain the batteries and consequently provoke a leakage.

But why alkaline batteries with the same age, brand and charge installed in simple flashlights with a mechanical switch seem to leak even when the switch is off and the flashlight is not used by a long time?

(This is a suspicion i have. I don't have enough data so i may be wrong)

Best Answer

Some switches themselves are to blame. Many cheap slide switches are simply two metal plates that slide over each other. Sometimes one is shaped with a curve to add a bit of spring action.

This type of switch is rife with friction, and sometimes there is dirt build-up and such. The device may turn "off" (a motor stops spinning) but there can actually still be leakage current because the switch plates didn't completely separate. They also may have completely separated, but over time the curved plate may flex due to vibration, temperature.

Moisture/humidity is another culprit that can affect these switches because they are not themselves enclosed.

Diagram of cheap sliding switch