Laste year, I picked up a bunch of B-grade A123 20ah LiFePO4 cells off of ebay, and painstakingly built a "48v" battery...
After some issues with my own ignorance and then issues with the BMS I had, I had to replaced cells as often as I used it. I've got it under control now, but I no longer have enough cells to make a second such battery.
This was how it looked:
I added further protection, in the form of low-voltage alarms made for RC batteries:
This is how it looks now:
It's trouble free at the moment, and it makes audible noise if any cell drop below 3V, so if I accidentally leave my ebike turned on again for some reason, I have a chance of preventing damage...
Specs: 20ah @ ~52V. BMS supposed limit: 100a peak, 50a continuous. I can get 30-40 km on a charge on my current e-bike, running at full speed, with a small passenger.
