Products specifying alkaline batteries

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.

 

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.

Puckdropper

 

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.

Michael

 

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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Hi...

The voltage of a brand new alkaline is 1.5 volts. The
voltage of a freshly charged nimh or nicd is 1.2 volts.

The likelihood is that your scale will see the 1.2 volts,
and decide that the battery is due for replacement - at worst
refuse to operate; at best tell you to change the battery.

Take care.

Ken

 

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.

CK

 

However, the terminal usable voltage of an alkaline will be very similar
to that of a Ni-Cad, etc.

 

I discovered recently that Duracell quote battery lifetime to 50% of initial
voltage ! Any rechargeable will be far better.

Graham

 

According to Duracell, an alkaline battery isn't dead until it reaches 0.75V !

Incidentally, you can get '9V' alkalines with 7 or 8 cells ( 8.4 or 9.6 V ).

Graham

 

You mean NiCd? Most "9V" rechareables are 7.2V. 9V alkaline batteries
consist of 6 1.5V cells which add up to an even 9V.

 

Does anyone MAKE a "9V" NiMH battery?

 

For an electronic scale,I'd use a wallwart.

 

Very good point!

 

actually,it's more like 1.4v

 

NiMH. I don't know what made me type alkaline !

I have one right here that I recharged a month or two ago and its current terminal
voltage is 8.99V.

Graham

 

I have one in front of me ( a cheapie ) that I recharged a month or two
back.

It currently measures 8.99V.

Graham

 

1.3 but not for long.

Graham

 

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?

noozer

 

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