Wattage of charger / voltage of pack = maximum charge current possible, EG:
50 / 25.2v (6s pack, fully charged voltage) = 1.98 amps.
Doesnt bother ne personally as I only do one session lasting a few hours - once all the batts are flat, thats the end of that days fun. For other people (racers?), then a 150-250 watt charger is needed to quickly recharge packs at a 1c or higher rate.
For a cheap and accurate 50watt charger, the Thunder Ac6 is getting good reviews
http://www.hobbypartz.com/thac6smbachw.html