I bought a Diamondback Recoil 29 (https://www.diamondback.com/recoil-49966) a few years ago and only recently decided to convert it to an e-bike using the BBSHD kit. I was leaning towards dual batteries simply because I would put them in a top tube bag like this one - Additive V2...
Thanks for the suggestions, but their mostly just bags that store on top of the top tube.
The V2 has side storage big enough to store 2x batteries which is very nice. It's a real shame that someone can't copy it and just sell a version as Additive themselves are a German company that doesn't...