I have a huge stack (400+ or so) of used AA Alkaline batteries (Duracell Industrial).
Remaining capacity left varies anywhere between 0% and about 30%.
I have no way of knowing which ones are really empty and which ones are at 30%.
I've got a couple of small gizmo's (containing a few LED's and a tiny DC-motor) that can be driven by any DC power-supply in the 4.5V-10V range and which draw only 10-20 mA current each.
I currently run these gizmo's from a USB charger wall-wart with a DIY Frankencable.
I would like to find a way to use those AA batteries in stead. Seems a waste to just send them in for recycling.
Putting 4 AA's in series would do the trick, but I'm well aware that putting mismatched batteries in series is potentially dangerous and certainly not efficient due to the weaker batteries having higher internal resistance.
Any ideas how to do it? Or is the 4 mismatched AA's in series not problematic enough to cause issues (besides draining the batteries quicker than normal)?
A way to identify the really empty ones would be nice too. (I'm using a 1.4V LED to test if a AA cell can light it up. But that only tells me which batteries are really dead.)