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.
I have been riding Ebikes the last 7 years. I built batteries from recycled 18650 cells, run commercial packs etc.
Since I have a long history with E r/c I run nothing but lipos as Im familiar with them and have multiple chargers.
Ive built many bikes, but have boiled down to one bike I have been running for the last several years. Its a 250w 24v geared hub motor running a 48v controller on 12s lipo. About 50v on full charge. I consistently over volt systems.
The motors dont care, controllers dont if you dont exceed 64v as thats the capacitors most controllers have, until you
get into the higher voltages. You just have to watch the low voltage cut on a particular controller so as not to pull
the batteries below the minimum voltage threshold. Advantage is deepest power density of the common battery chemistry. Also battery life. I have lipos still producing uasble capacity that are 5+ years old.
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.
I recently just bought an ebike and I'm digging it, now I just got to get learnt on how they work. Mines nothing fancy 36v 250watt I believe. I can already tell I want to go faster lol.View attachment 160445