This crank charger died after a few days. To open it there are 4 screws on the back side. After opening it turned up that charging setup is quite good. Good gears, motor, and rectifier circuit. The problem was in the rechargeable battery. The manufacturer used a cheap low quality battery which dies after a few charge rounds..(even a normal battery can perform a few charge rounds, but do not try that because some may explode or leak)...Lucky that I have so many rechargeable a batteries of different sizes. One from an old Motorola Bluetooth headset. It came perfect size to sit in place of the old battery. I did not snap a picture of the older battery before I throw it away in the battery recycle area.
One interesting observation is that you van reverse the use of this charger by using it as a geared motor. It has a good gear setup inside it, so if we connect 3.7-5 volts DC direct to the motor we can get a good movement by the crank lever to open a chicken feed door, or can entry ...etc.
Another worthwhile note is when you have any rechargeable item that broke or dies, do not throw simply. Shavers include a motor and battery to take. also chargers, cordless drills, Bluetooth sets, old cellphone...the harvest is worthwhile.