My Rayovac Hybrid NiMH batteries for my taillight get charged every couple of weeks. That is with daily use in the morning before sunrise. They are not fully drained at that point, but I want them charged before they become critically low or die (since the light is behind me and I wouldn't know when it quit working). My headlight is a Serfas True 250, with a lithium ion battery, and it gets charged nightly. It gets about two hours of use, with a one hour commute in the morning and the return trip home in the evening. I always have plenty of charge to spare, but prefer to start off each day's commute with a fully charged headlight in case I decide to take the scenic route to work.