no charge even though it says it's charging

I have a kindle fire HDX 7. I can use it if it's plugged in with my dell charger, but not with any other charger. I tried a hard reboot, but it did nothing. I then tried to do a factory reset, but it says I it cannot do it unless there is at least 30% charge. It says it's charging but there is no charge in the bar. I can use it as long as it's plugged in with my dell charger but once unplugged it turns off. bad battery?