Rechargeable Batteries - l-o-o-n-g

Dennis W. Farrell (
Wed, 15 Dec 1999 14:07:39 -0800

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West Wight Potter Website at URL
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There have been recent comments on the list about Rechargeable Alkaline
(RA) batteries for use in boat equipment such as VHF FM radios, depths
sounders, etc. Based on those comments (boy do I have faith in the people
on this list !) I bought 8 AA RA's and a small charger.

Experience: on the second charge cycle, the charger didn't shut off at full
charge and fried the batteries - internals came out all over the charger,
ruining both the batteries and the charger. I called Ray-O-Vac and without
question they replaced the ruined stuff with 2 sets of 4 batteries and a
full size charger. Very much a good corporate attitude.

Experience: My Kenwood TV-G7A ham HT can use four AA cells. Using freshly
charged RA's, the battery meter shows battery voltage to drop off
*significantly* when transmitting at the high power setting (~5 watts). I
haven't yet been able to tell how this affects my signal, but I would
imagine it's significantly reduced. Conclusion: use of RAs in VHF FM handy
talkies my not be a particularly good idea. At a minimum I'd recommend
range checks with RAs against other types of batteries to determine the
effects. Also see the next item.

Research: a collection of facts and observations.
The recommended peak draw on an RA should be less than 750 ma.Their capacity
is about 1000 mah when new, but this will drop to 500 - 700 (my
interpretation) ma after several charge cycles. There is little engineering
information available (at least outside the companies) regarding number if
cycles, depth of discharge, etc. due to the effect which the frequency and
depth of charge/discharge cycles has on battery life. NiCad AAs have at
most 1000 mah capacity, and NiMH AAs have about 1300 mah capacity. NiCads
have a nearly flat voltage discharge curve, while NiMHs show a *little* bit
more slope. NiCads self-discharge about 1% - 2%/day, while NiMHs self
discharge at about 1-1/2% to 3%/day. I don't know about the recommend peak
discharge current for either.

Suggestions/Recommendations for AA cells. Here's what I intend to do.
For VHF-FM hts use NiMH cells, keep them in the fridge in a plastic
bag/container between uses, and top up their charge just before putting into
service. Let them come to room temperature before charging. Note that NiMH
cells get a bit warmer than NiCads when charging. Second choice would be
NiCads, with Panasonic apparently having a bit better capacity than others.
Third choice and a desirable backup would be Alkaline cells, with Duracells
perhaps having more capacity than others.

For GPS's, use RAs and have a backup RA set available. For maximum cycle
life don't discharge more than about half-way, and recharge as soon as is

For flashlights, running lights, etc. I'd suggest NiCads, with RAs a second
choice as long as conditions are such that you don't run them dry before
charging. Alkalines will give a longer run time than RAs, but of course
can't be recharged for another go.

Your thoughts/comments/experiences?

-- dwf