The secrets of Eneloop batteries
In 2010 I bought a lot of Eneloop batteries, and these are in everything I use, AAA and AA.
These rechargable batteries are supposed to have very low self discharge, say still 80% full after a year, come charged, and are cool for in digital camera, as normal rechargables are always empty when you need them.
OK, some weeks ago, and I charge these with some Duracell charger, one cause the LED on the charger to flash indicating 'bad battery'. And indeed it would not even power my mp3 player. I had spare, but last week the second and third caused the same problem.
So, I ordered new ones, but kept those 'defective' batteries. Then yesterday, as I was very curious as to WHY those batteries 'failed', and the new batteries came with a link to
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I realized it could not have been too many charge-discharge cycles... So what? Put one on the voltmeter, no voltage ??? Well measured if it still did any short circuit current: 530 mA (AAA). that made no sense, no voltage - no current says Ohm. Tried the next one, exactly the same! Found voltmeter lead in probe was lose... Soldered it, 1.something volt, same current. That makes about 2 Ohm Ri, and not 20 milli Ohm as Eneloop claims. So they must then be simply EMPTY???? OK, put one on the lab supply, 80 mA for 16 hours, and voila, full again and working! But I did notice I had, to get 80 mA into that AAA, set for 1.6V or higher charging voltage. Studying the Eneloop datasheets (same site under pulldown menu), shows indeed that charging voltage may be as high as 1.7V for cold environment, and 1.6 for room temperature. The discharge voltage is normally higher than 1.2V, more like 1.28V for low loads. What I think happened is that the Duracell charger refused to charge above 1.5V, and that the cell, in spite of being empty, needed that much voltage. Or maybe me shorting it for the short circuit current test changed something in the cell. Anyways the things, with their higher output voltage than the normal 1.2V make for much longer use in my camera. But the claim that 'any' NiMH charger will charge them (>1000x) seems not correct. I will monitor these supposedly defective batteries for a while for self discharge and how long they last. So far that seems pretty good (mp3 player running all day on one). But battery chemistry will probably always be a bit of a mystery...