The Mi Band 5 and 4 each have a battery built in, which offers a very long battery life, but doesn't have a large capacity overall. Accordingly, it is possible that if you don't use the fitness bracelet that often, it can't be switched on anymore.
Mostly this is due to a deeply discharged battery that does not have enough voltage to start the tracker. In this case the following tips should help you to bring Mi Band 5 and 4 back to life:
Mi volume 5 and 4 to life - These tips help
A battery that has been deeply discharged must first be excited again with voltage. This excitation means that the Mi Band 5 or 4 must be attached to the charger and left there for at least 12 hours before the battery can be recharged.
It is often possible to recharge the battery after a short time, but this depends directly on how much the battery of the fitness tracker was deeply discharged.
If this method does not help and the Mi Band 5 and 4 still cannot be switched on or the display remains black, please use this workaround:
Place Fitness Tracker in the refrigerator
This approach is somewhat unconventional, but has brought Mi Band 5 and 4 back to life for many users.
To make this trick work, put the fitness bracelet in the refrigerator for about 10 hours. Attention: The temperature must not be below 0°C.
After the 10 hours have elapsed, please remove the bracelet and then attach it to the charger. Charging should now start immediately.
We hope that you were able to bring the bracelet back to life with one of the above tips and that you were able to charge the battery normally again.