The HTC One M8 battery is irremovable and bury underneath the motherboard, so if you want to replace a new one, you have to tear down the phone. You need to separate the M8 screen from front housing, then disassemble the battery. Here is step-by-step tutorial on how to change a HTC One M8 battery for your reference. http://www.etradesupply.com/blog/fix-a-cracked-htc-one-m8-screen/