I’m a live sound engineer by day and very novice electronics hobbyist. Hoping for some advice on a small project I'm attempting.
Although the use of rechargeable cells in my world are becoming more common, alkaline cells are still in heavy use for wireless audio transmitters and receivers. Unwilling to take the risk of a $1 cell running flat during a show, alkaline cells are changed each show. These half-used cells still have usable capacity, yet are thrown out or recycled. It's very common while working large cast theater shows <48 AA used cells are trashed or recycled each night.
In an effort to claim this unused energy from half spent alkaline batteries, I’ve been using a very simple rig using 4 “used” AA batteries which power a Li-ion USB charger which charges a single 18650 cell. I closely monitor the current draw, alkaline cell voltage and temperature. This 18650 cell is used in a larger battery pack to power other uses.
If trying to eliminate the risks of mixing cells of unknown capacity and age, could I use a singe AA cell with a DC to DC step-up (.9-1.5v to 5v) into a Li-ion charging type circuit (i.e. TP4056)?
If this is a viable path, is it dangerous or harmful for the 18650 to charge at a very low rate (>100mA) and/or long charging period?
Thanks for any insight and help.