I was wondering if there is a project out there that allows to use near-empty batteries, to charge a liion-battery.
The idea is that you often come across batteries that have not enough charge left to be used in the appropriate devices like a flashlight or mini-mixer. Now throwing them away would be a waste of energy, so is there some project out there that can harvest the leftover energy? The idea would be (optimally) an input voltage from 0V to 9V and an output that is capable of charging a liion-battery (4.2V ?). And then from the liion to a USB-port to charge any of the many devices that can be charged by it.
And if there are no leftover batterys maybe a solar panel or something like that.