I used to be pretty careful with battery charge but I found that it was too hard to tell when I should and shouldn't charge with time. At first I there was always something in the charger when I was trying to keep 6 NiMH batteries charged with a 4 slot charger and that didn't work too well. Now I'm using Li-ion batteries and usually charge after every ride or two and quit worrying about longevity due to huge increases in performance and decreases in replacement costs.