We use RC chargers with an integrated cell balancer. We don't balance them on the way down, but the cell monitors are an attempt to give us a warning if one cell is discharging faster than the others. In our limited practice at Barber, they tended to discharge evenly.
The A9 charger is actually an offshoot of a commercial agricultural sprayer drone charger designed for a specific 12s battery pack. The commercial version comes in a Pelican case and is nicely integrated with a big DC power supply, but is not programmable and only charges to 4.2v. You connect it and hit the big button and wait until the charging light goes out. We are charging to 4.1 and probably don't want to exceed 4.15, so I like the programmable RC chargers better. They are also cheaper. I have no idea why they put the 12s functionality in a consumer/hobbyist-grade charger; pretty much everywhere they use 12s batteries in the RC world they are wired up as 6s packs.
Single cell chargers would be impractical; we'd need hundreds of them.
Also, anything that requires a big-ass wiring harness is impractical; we have to swap out battery packs pretty frequently. Of course we could build something in to the battery pack, but then we'd need a lot of them, so it would have to be something cheap. Before this is over I expect to have 9-12 battery packs.
I've ordered a whole-pack charger (a small one that will do one 48v battery module for testing) and cheap balancer board, but the balancer board will probably blow up in actual use. Ricky tried one at Barber and it blew up, but a lot of stuff blew up at Barber. The other limitation of the cheap balancer board is that we can't use it as it was designed to be used; we pull too much power during operation, so we'd have to just use it during charging.
RC chargers are a problem. Looking at the failure mode of the chargers and discounting the one or two that my poor QC process probably damaged when I was building power and balancing connector harnesses for them, I'm guessing (guessing because I haven't done differential equations since high school and am probably not going to do any more real soon) that we have an inrush current problem with the output filtering capacitors when we connect the battery packs. It's rarely seen in the RC world (although I have found references to it in some drone forums) because the batteries/wires in the RC world can't supply enough current to blow too much stuff up. We have huge batteries (compared to RC batteries) and big wires, so we can blow up stuff pretty well. I'm experimenting with a pre-charge harness for the battery charge connection now and will do a lot more experimentation and testing before CMP.
Barber was a success in one aspect, we made the car fast, but I ran out of time after prepping the car to do proper QC on the charging solution, and that hurt us. Charging and batteries are my first priority for CMP.
Everybody grab your brooms, it's shenanigans!