Whether you need to charge it or not has mainly to do with the length of time you are planning on using it. If you need the extra half hour of burn time, then run the charge. Depending on the Cygolite you have, it may have a smart charger. I know the Cygolite Dualcross 300 that I have has the smart charger, but other lights that they make don't have the same device. If that is the case, be very attentive to the battery status as you do not want to overcharge it.