I bought a larger 4800 for longer runs. It takes about 1 hour 15 minutes. It can be charged more than 24 hours and still only lasts that long. If it is fully charged and the charger is not connected, it will be empty in 3-4 hours. The only way to do this is to keep it charged all the time except for 1 hour and 15 minutes when it works. Is the battery old? or what?