10 - 15 minutes
The phone would drop from 37% to 20% to 5% in less than a minute and go back up to 45% instantly when plugged in. Not at all reliable.
18 minutes with the tools included. Magical. The sucction cup part does require some faith but it works. Prying the battery was hard, my best bet was using the top spot. The instructions are excellent.
Followed the instructions and read all advice in there before each step. Every went smoothly. My phone now lasts 3 whole days without Bluetooth, easily 2 with my Pebble connected. Great improvement. Best 30$ spent.