It is normal for this battery chemistry to self-discharge over time. Otherwise stop charging when the battery shows full charge and check it over time and recharge only when needed. Many jumpstarters like this one can be charged through their 12 volt outlet without using the internal charger. New 'smart' microprocessor controlled charger/maintainers actually read the full charge voltage.and STOP CHARGIN G! They continue to periodically monitor the battery voltage and will needed charge it back up and repeat monitoring and charging only when needed. Sorry- this is just lead battery chemistry. This 2-3 volts will significantly lower the battery capacity or kill the battery over time. The problem is that non microprocessor chargers will kill the battery shortly after the warrantee period if they are left on!!! This unit uses a lead acid ,battery- if left charging at a voltage above 12.4 -13.6 volts the battery WILL BE DAMAGED FROM OVER_CHARGING!!! This jump-starter like may others will eventually float to over 15 volts. Charge your Ever start jump starter until the LED power indicator changes. If charging is successful, it will indicate at the LED digital display. Connect the charger into your car’s 12 volt DC accessory outlet. Insert the barrel connector of the 12V DC charger into your Everstart charging port. as I suspected the battery had been killed Most likely the previous owner followed the provided instructions and left it to 'float charge' the battery until it was needed. Duralast 10 Amp Battery Charger Instructions.
