Two months ago, I designed a small tool to collect the energy from the used battery. They may still have more than 70% energy inside even you cannot use them for normal cases. This simple device can rise the small voltage to 5 V which can be collected by a power station. Today I will tell you how to make a power charger. It can recharge the 18650 batteries. Also, it is a powerful power station that has a 7000 mAh capacity. You can adjust the output voltage to power your electric stuff. The voltage range covered from 5 V to 28 V. Hopes it will help you a little. Save energy, save the earth, from ourselves now. Keep safe this time.

https://youtu.be/90ZOef0z7G8