system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does every car have a different type of battery when every car takes a 12-Volt battery?
gpt
different sizes.

the bigger the engine, the bigger the amperage is needed for the electric starter motor to turn the engine.  the bigger the amp requirement, the bigger battery you need.

bigger batteries also happen to be more expensive and more heavy.   so you use the size battery that most appropriately matches your engine starting needs.