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This topic has been moved here
What made you think that it had anything to do with suggestions for the Arduino project ?
Please be more careful in future
I'd probably use a rechargeable 4S 14.8V Lipo battery for the motor. An L298N drops quite a lot of the supplied voltage so you need around 15V to have a reasonable chance of getting 12V at the motor.
The battery capacity (mAh) needed will depend on how long you expect the motors to run for. And you'll need a proper Lipo charger too.
There are many other options even a 12V lead-acid battery may work.
Steve
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@amethysthea - the next thing for you to learn about using the forum is not to put your replies inside the closing quote tag