With accumulation of AA rechargable cells I've bought over the years. Would be nice to make some kind of life tester.
I have been toying with the idea of some kind of resistor, for load. Also run a small clock on the cell. Start the clock at 12:00 and leave it to the next day. When the clock stops, that tells me for how many hours the battery was delivering power. 5:00 on the clock means 5 hours of power delivery.
The reason being so I could tell which batteries to trash, and which ones are still useful. Is any such device already made?