There are a lot of chargers with separate charging circuits for every slot. I've had good luck with an Opus brand charger. The one I have allows selecting char

There are a lot of chargers with separate charging circuits for every slot. I've had good luck with an Opus brand charger. The one I have allows selecting charging rates (200-1400 mA), and it has an LCD that tells you voltage, rate, status, etc. It also supports some discharge/refresh/test cycle stuff, although I don't know if the practicality of that is real. (If a battery isn't performing right, I feel like it's usually a lost cause.)