EM3ev has great batteries but doesn't make big packs anymore. DHGate.com has a lot of packs and sizes that will fit. It's WAY better to have one large battery than two smaller packs. I am using 3 large triangle packs (58.8V 1900 to 2000Wh each) that fit into my frame triangle. BBSxx mid-drives have a built-in controller that can use 58.8V with no modifications. There are also more and more custom build battery shops available you just have to search online.
If you start with a premium battery you can spend your time riding. I've always been one to do "the research" before getting into something (except wives for some reason), and I knew I'd be using BaFang BBSxx mid-drives because they have a built-in controller, can be mounted on almost any bike, are waterproof, and basically plug-n-play making them both simple and reliable. The BBS series can handle 60V out of the box so a 58.8V lithium pack using 18650s was going to give me the maximum amp-hours for the minimum weight that was available at the time. 35Ah pack at 58.8V is 2058Wh, I don't charge past 85% capacity (often) and I don't deplete them past 20% (ever) leaving 65% of the pack capacity or 1337Wh to use however I want without stressing the cells at all. A bonus is the larger a lithium pack the faster you can charge it without any stress to the cells. Using a Grin Satiator means I only need a single charger for different battery chemistries that lets me charge to whatever voltage I want at up to 8A and let the BMS do what it was designed for. I started with a 25Ah pack, bought another 29Ah and a 3rd 35Ah... all 58.8v. Adding a 300W solar panel and a voltage-boosting MPPT solar charge controller set at 56.8V means I don't have to monitor the charge and don't stress the cells. All my packs have had multiple hundreds of recharge cycles and it's not a question of "useable" capacity... I simply don't notice any difference in performance or in range. The only two things I would change if possible are to make the pack 100% waterproof and about 1/2 the weight. It sounds like sodium-ion batteries are going to be much lighter but not as efficient as lithium-ion are at this point. Until then... I'll just keep riding.
www.btrpower.com
1000w bbshd mid drive on that and you wont look back bro.
