I don't know. I've read criticism about fast chargers, and recommendations for the sophisticated chargers that check/discharge/condition and recharge each cell individually, but I've never tried one. All my batteries have been recharged in whatever cheap/free unit came with them and I haven't had any problems.
Does it really matter, or only if you're shooting and recharging a lot? I reckon I can buy a lot of batteries for the price of one of these units, so I don't particularly care if I'm shortening their life span.