This is an excellent question and the answer is very simple: EVERY NIGHT. Each and every day you use your mobility device, it should be recharged that evening. Whether it was just to the mail box or a full day at the fair, plug it in before bed and it will be ready to go in the morning. Overcharging concerns are long gone with the technology inside the new chargers these days. NOTE: If you have not used your mobility device for more than 7-days, it should STILL be charged. We suggest a routine of once a week, especially during the winter months. Batteries that are neglected for more than a few weeks will begin to have a reduced life span. Protect your investment and charge your batteries frequently.