I have a Rocky Mountain Fusion 10 mountain bike that I'd like to convert. Here's a link.
As you can see, the frame is pretty cramped. I'm not sure I can mount a battery in there. Is there a mini battery available? Is installing a rear rack for a battery a good choice?
I recommend using the Bafang USA Direct website to help with this. For each battery size, they have a handy pdf file that is a printable template of the battery size. You can print out this template and use it to test fit before actually buying a battery. Battery sizes are pretty standard so once you find a size that works, you should be able to shop with Johnny or elsewhere for the actual battery. Very useful of feature of that site.
you would measure your triangle mounting space and see if a battery fits inside it. if not, look into custom batteries.
https://bicyclemotorworks.com/product-category/e-bike-batteries/52v/
i cringe whenever i see the heaviest component on the bike, the battery sitting on a rear rack. depending on what your doing, big bumps with that weight on the rear rack gets annoying. suggest avoid doing that.