I have several used 18650 batteries from my old laptop battery. They all look OK, I have charged them and discharged. The capacity is around 1700 mAh, nominal capacity was 2500 mAh when new.
I'm thinking about how to use them.
There is wall clock in kids bedroom. I'm about to add some LEDs to it so the clock is slightly illuminated during night. Just a little bit so it is not too bright to disturb sleeping but it is just bright enough to barely see clock hands. The current consumption will be around 1 mA.
But I am pretty worried about safety, which is priority #1 for me. The last thing I want is to put a "incendiary bomb" in kids bedroom. Is there a risk that 18650 battery can explode or catch fire in this situation? Or is it better to use 4 NiMH batteries instead? (and dispose my old 18650 batteries).