Rechargeable battery issue

Not so much an issue, more of a mystery.

I have a number of rechargeable high capacity (2700 and 2900 mAh) NiMH AA batteries. For various reasons these don't get used very often nowadays, and when I went to them they seemed non functional. The battery charger that was supplied with some of them seemed to indicate that they wouldn't charge, and a multimeter was showing an output of 0.

Out of curiosity as much as anything I put the first lot of four, 'Powerex' 2700, in a generic NiMH charger and let them cooking for a couple of hours. They looked to be still charging, but I took them out to check the voltage and it was still zero. Put them back in and after some flickering the charger indicated they were done. I took them out and tried the meter again, this time they all showed 1.46 volts.

Next batch was a set of Vapex 2900 mAh. Again, zero volts on the meter. I put them in the charger and watched as the LCD display went from zero to ready in about 10-15 minutes. I checked them with the meter and once again, 1.46 volts.

With the Vapex I wondered if there was some gross memory effect, so I put them in my ist DS and proceeded to hammer it through about 350 exposures, with flash, which it endured quite happily. When I first put them in, the battery indicator showed full, but very quickly showed empty, but the camera kept going. I switched it off then back on and the camera's battery indicator showed full for the remained of the experiment.

So, fingers crossed that they are all sorted. Hopefully this might be of help to anyone with a similar problem (if, indeed, mine is cured!) But it would be nice to hear the opinions of a battery expert on this experience.

You should never let the batteries fall to 0v. They can sometimes be brought back to life... oddly usually in a cheap charger for a few seconds. Most of the the better chargers won't charge a 0v battery.
But once the battery shows a small voltage the better chargers will do a better job and go through a charge/discharge cycle.

I have read somewhere that it's possible to trick a better charger into thinking that a 0v battery has a voltage. I think it just involves starting the charge with a good battery and quickly swapping it for the 0v battery.

I charge/discharge all my batteries every few months with a La Crosse type charger shown here.......

http://www.youtube.com/watch?v=chdy5iJ0FnU

Mine's actually a Technoline BL-700 available for about £32 on
Amazon.

It's important to know the actual capacity of old batteries some
might be down to below 1000 mAh.



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One trick for "jump starting" an otherwise dead/empty battery is to connect another battery to it (I use a 9V battery) for a few seconds, + to + and - to -.

It pushes a little bit of a charge into the 'dead' battery that 'fools' the charger into charging again.

You might need to do it a few times before it works.