On Mon, 08 May 2006 00:08:21 -0700, Roy Lewallen wrote:

|Dave Fawthrop wrote:
| On Sun, 07 May 2006 19:39:13 +0100, Owain
| wrote:
|
| |Guy King wrote:
| |Until Alkaline battery manufacturers state the Ampere hour capacity on each
| |battery, I will believe that they are all the same and buy the cheapest
| |available.
| | Their argument against doing this is that the effective Ah rate of each
| | cell differs at different discharge rates and that comparing like with
| | like wouldn't be possible.
| |
| |But doesn't the Ah rate of nicads vary in the same way?
|
| The same thing happens with *all* batteries whatever the Chemistry.
|
| NiMhs give a single figure, why not Alkalines?
|
|NiMh capacity varies only a relatively small amount over a very wide
|range of load conditions. By comparison, alkalines vary a whole lot. The
|amount you can get out of one depends heavily not only on the discharge
|rate, but how long the cell is allowed to rest in between partial
|discharges. Also, cells can be optimized for light or heavy discharge
|rates, so one which does better at low rates might do worse at high rates.
|
|You can be sure that if manufacturers were pressed to come up with a
|single number for alkaline cell capacity, each would set up the test at
|the most favorable condition for their particular cell (and then inflate
|the result, like they all do for NiMh cells). The resulting numbers
|would be totally useless.

Not IMI totally useless, just limited. Better than the nothing which the
average buyer, who would not understand the data sheets, has at the moment.
Then an international standards body should set up the test method.
--
Dave Fawthrop dave hyphenologist co uk Google Groups is IME the *worst*
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