GoPro HERO4 Silver Mode D'emploi page 72

/ Battery
The battery charges to 80% in approximately one hour and 100% in
approximately two hours when using GoPro's USB-compatible Wall
or Auto Charger.
You can also charge the battery outside of the camera using the Dual
Battery Charger (sold separately).
No damage occurs to the camera or battery if used prior to full charge.
Spare batteries and additional charging accessories are available at
gopro.com.
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