Two Letters Re: NiMH Batteries

Jim:

If left idle, a NiMH battery loses up to 1% of its original capacity per day. (This doesn’t mean that it loses 100% in 100 days; rather, it means that after day one, it is at 99%, after day 2, it may be at 98.01%, etc. — it will theoretically never reach 0%)

I bought a Grundig/Eton FRS250 hand crank radio a year ago. I used it every day for about two months and it would run for two or three hours on a two-minute crank. I then left it idle for about 8 months, after which time it would only play for about 10 minutes on a two minute crank. Needless to say, this is highly disappointing and constitutes a major flaw for preparation. (What good is an emergency hand crank radio if it doesn’t work in an emergency?)

To (hopefully) remedy this problem, I recently ordered an adaptor/charger from the manufacturer (Eton). If you hook up the radio to the adaptor/charger and leave it plugged in, it will send a low-voltage trickle charge to the batteries to keep them “topped off.” In theory, this should drastically extend the life of the batteries. Time will tell. If, six months from now, I can get still a few hours of play time on a full crank, then I will conclude that the trickle charger is the best solution to the NiMH problem. (Note that it is possible to “fry” NiMH batteries if the trickle charger is too powerful, so do your homework if you are shopping for one.)

Frankly, as popular as hand crank emergency radios have become, I am surprised that I have never read about this flaw in reviews and discussions. A lot of people who bought these radios and keep ’em in the box are going to be sorely disappointed when the lights go out and discover that their radio doesn’t work because the batteries are nearly dead. (Of course, even if the batteries are dead, the radio will still play if yo u constantly turn the crank, but that doesn’t sound too fun.)

Moral of the story: stock up on alkaline batteries just in case. – J.S. in Virginia

Hi Jim,
Regarding the question on the blog about storing NiMH batteries. Basically they do not store very well. Nor do they seem to last as long as they are advertised to. My company makes industrial equipment that uses small (2 AA cell equivalent capacity) NiMH battery packs. When we first started using them, we believed that they would last for five+ years and hundreds, if not thousands, of charge/discharge cycles. That was an expensive assumption for us. We have found them to last only for several hundred cycles and they tend to fail even before that number of charges if they are kept on a trickle charger. It also takes several charge/discharge cycles before they work at full capacity. We have also had a lot of failures with new batteries that have been sitting on the shelf for a year or so. In a survival situation, NiMH batteries self discharge from fully charged to empty in two-to-three months, so in a survival situation you will be starting with batteries of unknown charge. I generally would recommend against them. I have a bunch of NiMH AA cells for my camera, but the only practical way to charge them is using a charger plugged into my car. If you want to go solar, it will take will take a five watt solar panel of power and about a half a day to charge four typical AA NiMH cells of 2000 maH hours plus. My plans are built around my supply of alkaline AA/AAA cells that I rotate through every couple of years. I’m confident that even if they sit for 5 years in my refrigerator, my batteries will still have a good amount of available power. Regards, – P. Smith