For a phone I got second hand whos battery was never all that great, I had been on the fence about replacing it. Using AccuBattery, I found that my 3300Mah was all the way down to barely 1000Mah... not bad for a 6 year old battery. I replaced it myself, and the battery was COMPLETELY DRAINED! Some batteries have at least *some* charge.. not this one. After fully charging, and using as much as I do, AccuBattery is reporting slightly over 2700Mah. For a battery that hasnt been in production for a very long time (and I suspect this was an OEM battery... serial numbers looked like they came from the same line, just 9 or so months after mine did) It has a VERY usable life left. The OnePlus 5T is still a very capable phone, and being able to give it a few more years of life for only $27, I'm quite happy.