BenQ M300 - Manual (Page 16)

2 Preparing Your Phone For Use
Installing the Battery
1. Place the battery onto the back of the phone, with the battery's
contacts facing downwards and the tab on its top edge in alignment
with the holes in the battery compartment.
2. Push the battery against the top of the compartment and press it
down to click it into the compartment.
Installing the Back Cover
Place the back cover onto the back of your phone and slide forward
until the latch catches the cover.
Do not remove the battery when the phone is on. Doing so could
cause you to lose personal settings or data stored either on your SIM
card or in the phone's memory.