system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: How does a battery company produce say a double A battery that's better or worse than a competitor if it's the same thing?

Do generic products just like add less juice and more popular ones add more or something?
gpt
Firstly there are several different chemistries that are used in AA batteries. Some are more expensive and have higher capacity than others.

The consider that a battery is not just a pot of chemicals. There are various components including a carbon anode, separator, exterior can etc. The quality of these affects the capacity and internal resistance of the battery.

Edit to add: rechargeable batteries have even more variation because the robustness of different geometries to repeated cycling is not trivial to optimise.