18650 the new battery measures 4 volts, ok?

In the past, the target of the old version of 18650 was 3.6V (including the previous lithium polymer battery), and now the target is 3.7V. This voltage is actually the electromotive force of the battery, which is determined by the battery material. 18650 is actually a lithium battery. Now almost all mobile phone batteries are lithium polymer batteries. However, their charging cut-off voltages are the same, and they can be used interchangeably, so there is generally no big problem.

I want to know what your charger is like. If you use the original mobile phone charger, that's the best. Many forum players change their mobile phone chargers to 18650 chargers, among which Samsung charger is the most talked about (personal understanding only). If it is universal charging, it can actually be used, but it is not good for the battery. On the surface, the most direct thing is that the cut-off voltage is not accurate. In many cases, the cut-off voltage is too high, resulting in overcharge of the battery. Yours is 4V, obviously the voltage is too high, and it is easy to burn the board.