I am using 3x 12v 185wh batteries in series. Realistically I can count on around 500wh. They are only 3 lbs each and fit neatly within the frame of the mtb. I don't like having them up on the rear rack, they tend to make the tail of the bike wag a bit compared to low and centered.

https://old.reddit.com/r/ebikes/comments/1o0qthk/dynagirl_ri...

I just 3d printed protective covers for them last week when marketing turned their back on the new Bambu printer.