BE ) writes:
On 10/11/06 6:52 PM, in article ,
"Jim Yanik" wrote:

Meat Plow wrote in
news
On Wed, 11 Oct 2006 14:47:28 +0000, BE Has Frothed:

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.

Thanks,
noozer

As they discharge, the voltage drops off more linear in an alkaline.
The rechargable stays more constant then drops off rapidly. Hence the
scale will operate longer on an alkaline.


Does anyone MAKE a "9V" NiMH battery?

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?

Because it's a chemical matter.

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.

Michael