I ordered this replacement battery from Amazon advertised to fit the MyTouch 4G, which is basically the same phone as the Thunderbolt. It was advertised as an OEM battery, but it was so cheap I suspected it to be a clone; boy was I surprised when it arrived the next day (Amazon Prime is the bomb!). The battery was, in fact, a genuine HTC battery. It popped right into my Thunderbolt with one minor difference – the logo faces in, towards the screen of the phone, vs out, towards the battery cover. It is functionally perfect and the battery life is outstanding – I forgot my battery life was actually good at one time! The random resets have also vanished. All in all, this was a great buy and I might buy another for a backup; you should too!