This could be damage to the battery connector or the battery flex—-if the battery can’t communicate it’s data to the logic board (the tiny center pins of the battery) then the phone will reboot every three minutes and report incorrect battery percentage.[br]
[br]
The other likely case is that this isn’t bad battery at all, but instead “charger damage” You can get damage to the charger facing chips, tristar and tigris, by using non-certified charging cables. To check if this is the problem you need a usb ammeter—this device will tell you if it is consuming normal charging current or not.