I really wouldn't go past 48 cells with a 144 volt controller. 50 may be O.K. but voltage at the bleeding upper limits are quite hard on the controller. 45 cells is most often billed as a 144 volt pack. With 50 cells you will be hitting the throttle many times at 3.35 volts per cell but that kind of voltage would only happen once at startup with 12 lead acid batteries. The ripple and the electrolytic caps -- seems like a way to early controller death (and even the Curtis is expensive.)