I am planning on building an ~60V, ~50A, 18650 battery pack to power a 2 kW electric motor. I've called some electronics stores and it seems like I can get a decent amount of old laptop batteries for free. The obvious problem is that each cell is going to have different lifetimes, capacities, resistances etc. so ill need some way to balance them.
How can I make what is probably going to be the most hack battery ever, as reliable as possible? Should I buy a few BMS's and try and balance each individual cell? should I balance each parallel group? should I not even bother trying this and shell out money for real batteries?