I have an electronic scale that uses a 9v battery and it says "use alkaline batteries only". I prefer to use rechargeable NiMH batteries. How can the product tell the difference (or can it) and what would be the problem, if any, of using non-alkaline batteries in such a product.
BE wrote in news:C1526E2D.571DD%n3wsr3ad3r_|@|_sbcglobal.net:
Rechargable batteries tend to have a lower voltage than non-rechargable, so the voltage difference might cause trouble. My guess is the "Use alkaline batteries only" is there because the manufacturer knows the device likes to eat batteries for breakfast, lunch, and dinner.
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Maybe more important, rechargeables don't start with the same voltage level as fresh alkalines, and if the unit counts on the voltage being above a certain point, the useable "life" of the rechargeable will not be so long (though of course, they can be recharged).
I used to have something, it might have been my Radio Shack Model
100 laptop, that I used rechargeables in, and they sure didn't last as long as alkalines. On the other hand, the rechargeables could be recharged so I got more long term life out of them than the alkalines.
The bottom line is it almost certainly won't hurt the equipment so may be worth trying. For something like an electronic scale, rechargeables may indeed be fine.
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Or pehaps the current drain is so low that alkalines will last for years, and rechargables will self discharge in days to weeks. For low drain devices like clocks, calculators, and scales with LCD displays, or other infrequently used devices, rechargables do not really make sense. Alkalines have a shelf life of several years.
I just bought several Energizer Rechargeable "9v" batteries (NiMH) and, thanks to a previous post, I looked at the fine print and, yes, it is actually 7.2volts! It says: "Size 9v" - so they can claim it is a 9v battery due to the loose use of the term "9v" to indicate a "size" rather than a power potential.
Why would the makers of these rechargeables make them not truly match the voltage they are supposed to be?
A cell puts out about 1.5v. If you need more voltage, you combine them. So when the need for 9v batteries came along, they had to combine six cells in the package. Or maybe they decided on package size, and then picked a voltage that would fit the package. Open up a 9v battery, and you'll see six invidual cells. In some, it's 6 sort of lumps, but in others it's sort of like skinny AAA cells inside. If they needed more voltage, they'd have to add more cells, and the package would be bigger for the same amount of current.
Nicads put out about 1.2v. That too is a chemical issue. The only way they can get a higher voltage is by combining cells in the same package, but that cuts current capacity (since the cells would be smaller), and results in not the needed 1.5v but 2.4 volts.
So when they combine 6 nicad cells in a "9v battery" package,
6 * 1.2 =7.2volts. Again, the only way to fix that is by putting mroe cells inside that package, and while that's more feasible than with a straight AA cell, it forces each to be a physically smaller cell and that likely impacts on the current the whole thing can supply.
In some cases, equipment has been designed with all this in mind. The battery compartment will be big enough to accomodate more batteries than the needed voltage would require in alkaline batteries. So that old CB walkie talkie would have a place for 10 AA batteries, so if they are nicads it gets 12v. It would then come with a pair of dummy AAs, that merely fill space and provide contact end to end, so when using alkaline AAs you would simply put in 10 AAs and the dummies, and still get 12volts.