When using it for the first time charge the toothbrush.

The suitable temperature is between 5 degrees and 35 degrees, temperatures outside of this range my cause charging difficulties. It is normal for the temperature to rise a little during use and charging.
 
Charging Instructions
 
1 Charging time is about 7 hours
2 The charging state mode light enters the blinking state, and turns off after 3 seconds, entering the charging state
3 When the green light stays on, the charging is complete
4 The yellow light indicates if the battery is low
5 Power bars : 5 LED lights are on at the same time, indicates the power exceeds 90%;
If it is 4 lights, the capacity is over 75% If it is 3 lights, the capacity is over 50%; 2 lights are on, the capacity is over 25%; 1 light is on, the capacity is over 15%.
When the yellow light is on, it means the battery is lower than 10%, and the reminder will be repeated 4 times.