I've had the pack built for a couple months and it's been running great. I built it using Samsung 21700 40T cells with N.E.S.E. modules that you don't have to solder. They work great and I highly recommend them if you guys want to built battery packs without having to solder tabs together. Here's a link to his site:
18650.lt
He's got the modules available to 3D print yourself or you can can purchase from him. My brother has a good 3D printer so I just had him print the modules for me. Here's some pics of the battery build process. I used 14 of the 4 cell modules to make a 52v pack. This is what the modules looked like opened up. You just insert the batteries inside and they are pressure fit.
Here's the pack arranged with the BMS wires attached.
I used a XT90 anti-spark for the main connection with a XT60 for the charge cable. I connect the XT60 charge cable is connected to the stock XLR charge port.
Here's how everything is mounted.
The pack fits perfectly in the bottom tray, I used a cheap dollar store cutting board as extra insulation on the top of the pack. I was even able to use the stock battery bracket but with longer screws. I mounted the controller diagonally in the tray with a rubber reusable zip-tie.
Everything fits inside the stock case perfectly.
The pack fully charged is 58.8 volts and I top out at ~27mph according to GPS. This is all with stock gearing. I've been on the stock chain for a few years on the 48v lead acid setup and I've had no issues. So far it's been fine on the 52v lithium setup.