LG G3 User Manual page 19

The Basics
19
Step 2. Insert the Battery
Insert the battery in its compartment, making sure to align the gold
contacts. Press down gently to secure the battery.
Step 3. Replace the Back Cover
Place the cover over the back of the phone, then press down along the
edges to secure the cover.
Step 4. Charge the Phone
Before turning on your phone, fully charge the battery. Be sure to use the
USB Cable and Charger Adapter that came with your phone. Correctly
orient the USB Cable plug before inserting it in the USB/Charger Port to
avoid damage to your phone. See Charging the Phone on page 23 for
more information.