system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why shouldn't you mix different battery brands?

A lot of electronics that require batteries recommend that you shouldn't use batteries of different types or brands. I understand why you wouldn't want to use batteries of different voltages but why do brands matter?
gpt
Different brands can have different design and capacity.

Ideally you shouldn't mix cells of different chemistry, maximum capacity, and state of charge. The reason is that you want the cells to have the same voltage, and maintain similar voltage as they discharge. If one dies sooner than the others, it can leak caustic electrolyte. Plus the other cells are likely to be replaced prematurely. 

Edit : changed "current capacity" to "state of charge". 

"current capacity" is ambiguous.