Where would you put the battery ?

[TheAntidote]

 

[JES2020]

If you are wanting a larger battery, you want it lower on the bike to help with stability.
You have a lot of space under the frame behind the front wheel, or you could put a smaller one, rear of the seat post and under top bar.

 

[Slaphappygamer]

Depends on the size of battery you are wanting to work with. A 36v triangle battery could probably fit in the triangle just above the pedals. Are you planning to install a mid drive motor?

 

[fauconnier]

Fist place that came to my mind.