Verykool i800 - Manual (Page 67)

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consume power, which shortens the standby duration. Either use
your phone in a stronger signal area or switch it off temporarily.

Your battery may need to be changed.
The battery does not charge properly

Make sure the plug is well connected.

Wipe the charging contacts both on the phone and on the battery
with a clean soft cloth.

When charging in an environment below 0℃(32°F) or above 45℃
(110°F), change your charging environment.

Change the battery or charger which is damaged.
If the above guidelines do not help you to solve the problem, take note of
the model and serial numbers of your phone, your warranty details and a
clear description of the problem. Then contact your local after-sales
service.