What does "do not mix different types of battery" actually mean?

[BelfastSmile]

Trying to get one of DS' toys operational, and I've been hunting around for batteries. But they all say "Do not mix different types of batteries"... I usually buy exactly the same batteries anyway, so it's never been an issue, but today I have a mixture and it occurred to me that I don't really know what they mean by "different types".

Do that mean "don't mix rechargeable and non-rechargeable"? Or "Tesco and Duracell"? Or "Long life and regular"?

What are the "types" that can't be mixed?

They mean don't mix different brands and the recommendation is that you shouldn't mix old and new either. Apparently it can affect performance or even cause rupture or leakage.

I thought it meant don't mix rechargeable and non-rechargeable.

I'm interested to know.

I think it means use exactly the same ones, I'm pretty sure that's been a thing even before non-rechargable batteries were in common use but realistically nothing terrible is going to happen if you mix and match the thing might not work as well afaik but what else could go wrong?

Mixing different brands should be OK as long as they are the same voltage and output (mah).

Don't mix different battery types - e.g rechargable NiMh with disposable Alkaline because that can cause leakage and damage to the thing they are charging. Leakage can also burn / irritate skin.

Don't mix old and new disposable batteries in a toy if possible because one dead cell stops the current so you end up having to replace more often, and unless you test the batteries you are are throwing away otherwise usable batteries with the dud old one.

Thanks everyone! Good to know! Is there also something about not using old and new rechargeable batteries together?