Provided that the battery is not open-circuit, even if it just can't be properly charged for any reason, then connecting it to a power source [DC car charger, AC wall charger, 5v USB] will allow it to turn on. If the battery is open-circuit or missing then in my experience the unit will not power up regardless. So if it won't power up connected to a power source and the battery doesn't charge and continues to show 0% even after connection to a charging source for quite some time, then it's kuput and you you should replace it. After-market batteries are cheap and quite easy to change in 1xxx series. [i.e. what Caty said].