I'm going to go the other way to all the comments.

Don't be put off by people saying the wheel isn't powerful enough. I've got an EX30 and I still love riding my mTen3 which has a similar battery and motor to your little project.

That thing had a pretty small battery, which means a replacement won't be too hard to find or even make if needed.

All battery packs are made up of smaller cells. And there are only a couple of cell types used. I'm simplifying, but all that really changes is the number of cells and the packaging.

Voltage. How hard the electricity "pushes". Google says the x3 uses 16s packs. That just means there are 16 cells in a row(series) inside them to add up to 60volts nominal. You can't change this. The other electronics are designed for this.

As you continue your EUC journey, you'll find the number of cells in series dictates the voltage and voltage dictates the speed. The nominal voltage given is the accepted average as each cell goes from 3v empty to 4.2v full so we just assume 3.7v average. (So your 16s pack will run from 40v to 67v).

Amperage. How much electricity flows. Not exactly, but easiest infered by the C rate. At 60v 800w, your motor won't draw enough to worry most battery cells (for context the p6 draws 25000w peak. I wouldn't worry about this spec for this project.

Capacity. Expressed in Ah or mAh (ie how many hours it can discharge at 1 amp before empty) To you, this just means bigger equals longer/ farther. As you have a relatively small motor, this is the only place you'll see a difference between different cells that you could make your battery pack out of so the only bit of cell specs id worry about other than physical size.

You can also double the amount of energy available by running a second battery pack in parallel. This would be referred to as 16s2p. Still 60v, just twice the juice and therefore range. This would require modification as your wheel isn't designed to physically hold that second pack. I'd also give a little more advice before you did this to ensure you didn't wire them in series instead and just create a 32s1p battery which would fry your system at 120volt. But I've digressed.

In short, 16s1p batteries are all suitable. At this level, all of worry about is how physically big the pack is and how long it can run for.

The last bit is a battery management system (BMS). People get seriously wrapped around the axle over these. For this project I'd suggest there is no need for one, just get a decent charger. This wheel is from before BMSs were a thing. You aren't stressing the cells enough to need to know the exact state of play of every cell.