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Why do alkaline batteries sometimes leak?

Question to Knivesandtools:

The alkaline batteries in my torch started to leak. How is that possible?

Answer of Knivesandtools:

Powerful LED torches burden penlite batteries heavily. We measured loads of up to 2.7 Ampère and that is a lot!

Alkaline batteries can deliver that power for a short time, but their high inner resistance causes them to empty a lot faster than expected and they can become very warm.

We have measured temperatures of 64 degrees in a Fenix L2D (type from 2008) and 55 degrees in the newer LD20 models (type from 2011).

In the latter, the more modern LED generates less heat which means the batteries become less warm.

The high charge and too high temperature of the batteries increase the risk of leakage of the batteries enormously which means leaking batteries in torches occur a lot more often than in a clock for example.

Leakage also occurs regularly in A brands like Duracell and Energizer.

Consequences of leakage of alkaline batteries

The consequences of the leakage can be serious. The alkaline fluid that leaks out of an alkaline battery seriously damage aluminium.

The switch of a torch, in particular, gets damaged quickly. Sometimes torches are even returned to us in which the batteries are stuck in the casing because of leakage.

Preventing leakage

The best way to prevent leakage of Alkaline batteries is to use other batteries.

Rechargeable NiMH batteries are the most obvious choice.

They are powerful and do not leak. Read more about rechargeable NiMH batteries here.

If you still want to use alkaline batteries, bear in mind that they could leak.

Therefore, always remove the batteries from the torch when not in use, and immediately replace empty batteries.

Never mix used batteries with new or other brand batteries. That considerably increases the leakage risk.


Empty batteries are chemical waste. Don't throw them in the dustbin but return them to a DIY store or a collection point for chemical waste. A small effort and a great benefit to many.

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