Have been buying a bunch of those standard 9V batteries (a few different
brands) over the past few months, and have noticed that instead of 9V they
have been measuring out, with a VOM, at around 10.0 to 10.25. This is under
Anyone else notice this ?
Was wondering if this might be the cause of all the problems I've been
having with my fire alarms
giving 3 to 4 chirps, around once a day ?
It's probably the same type of chirp signal that the unit gives when the
batteries are low.
Don't believe voltage changes with load. Amperage is number to
Electromotive potential determines voltage. If you open up a standard
9 volt battery you will find 6 1.5 volt batteries in series.
Battery's voltage will depend on materials it is made from. Alkaline
batteries will vary from the standard 1.5 volts of old carbon/zinc
You're kidding right? Amperage goes up with load. Amperage IS load. Where
capacity is limited, no load voltage will always be higher than loaded
Amperage goes down with resistance; is that what you meant?
If you open up a battery you will find cells. That is the definition of a
battery; a group of cells. I expect there are instances where you would
find batteries in batteries, but that would be unusual.
Capacity is always limited. Voltage only stays constant with load with
voltage regulated supplies that are not loaded to capacity.
To "load" something means to increase the current flowing through it.
Amperage does indeed go up with load (usually).
Put a volt meter across your 12V car battery. If it reads 12V, your battery
is "dead" and probably won't start the engine. An open circuit car battery
in good condition that hasn't been recently charged will have ~12.6 V.
across the terminals.
I was trying to address the battery chemistry itself. Available
voltage depends on the cell potential, i.e. the redox chemistry of the
chemical electrodes. The best you can do with chemicals is about 6
volts. This is why you need cells in series.
There is a concentration dependence which accounts for voltage drop
with time. But amperage is dependent on the total concentration of
ingredients. You look at it like water pressure through large and
small pipes. At equal pressure, you're going to get a lot more water
through the big pipe. That's amperage. If all you needed was
voltage, then you could replace the big lead acid battery in your car
with eight triple A rechargeable batteries.
That said, I put my VOM to a new 9 volt alkaline battery and it
measured 9 volts. Did not leave it hooked up to see how long that
would last. I did note that a lot of newer rechargeable batteries are
less than the voltage of the batteries they replace. Most modern
stuff will handle them.
I agree with you in principle but I've come to accept the fact that
definitions evolve and words mean what people want them to mean. Thus (and
unfortunately) it has become acceptable to refer to a single power cell as
One would hope, however, that when the apparently indivisible (to a
layperson) unit is indeed composed of several sub-units (and by this I mean
car batteries, 9V batteries, etc.) we might at least in this instance
continue to refer to the sub-units as cells and not batteries within
But it's an unwinnable war. Someday I fully expect the term "it's" to
become fully acceptable in standard English in the possessive sense and
then the barbarians will have won. In the meantime I wish web forum
software would come with a plug-in that would, on displaying posted text,
randomly convert "it's" into "it is". Correct users will still be correct
if a bit stilted. Incorrect users will be made to look moronic.
On 7 May 2007 09:54:11 -0700, Frank wrote:
Because a battery has an internal resistance, when placed in a circuit with
a load, it's effective (which is what you will measure with a meter)
voltage will drop.
Battery voltage is only "nominal" or approximate. An old type battery, a
carbon/zinc was nominally rated at 1.5 volts but actually under no load put
out 1.7 volts, other types will vary. A car lead/acid battery actually puts
out 2.2 volts per cell. When cars used 6 volt batteries they used 3 cells
which actually gave 6.6 volts or a nominal 6 volts. Today's car batteries
out a nominal 12 volts which is actually 14.2 volts.
Since the battery has resistance as the load increases the voltage will
drop. If the battery had no resistance you would be correct.
My guess is the OP is using a digital meter and is finding he gets
different results since the resistance of the meter is so much higher than
the old analog meters. Of course part of the problem is likely to be as you
correctly pointed out the measured voltage of different kinds of batteries
That would be an IDEAL voltage source (and, of course, ideal things
A REAL voltage source behaves as an ideal voltage source in series
with a resistor. This resistance (the cell resistance, not a separate
component) is in series with the load. In this way, voltage at the
battery terminals will vary with load. As the battery discharges, its
internal resistance increases, causing a greater voltage drop when a
load is applied.
Not "determines", "is". "Voltage" is a name for electromotive
potential. This explains the use of the symbol 'E' for voltage.
True of fully charged cells with no load, although the numbers ARE
Not me, but I haven't been measuring lately. See further down.
Batteries themselves have internal resistance. I suppose, if you
measure the amperage in the circuit, and you measure the difference in
battery voltage with no current, and the battery voltage with that
amperage, you can find the voltage drop and calculate the internal
resistance. Although I'm not sure if it constant at all current
Different chemical reactions create different voltages. There are
chemical reactions at both poles of a cell, and the sum of the two
voltages with carbon-zinc batteries is about 1.5. When they wanted
to make other kinds of batteries, that would be the same size and work
in the same devices that carbon-zinc batteries did, they tried to come
up with pairs of reactions that would also total 1.5 or close.
I'm wondering if the batteries that Robert1 has might have been made
with different from the normal chemicals, to save money I suppose, and
that is why their voltage is so high. Sort of like some Chinese
manufacturer put melamine in dog food to raise the apparent protein
content. (Because melamine has some ingredient that increases some
measurement on tests.)
R, you say a bunch of different brands. Does that include name
brands? What brands? Lots of off brands are made by the same
company. Even name brands can be forged, or some manager might do
something to make extra for himself.
A battery cell is a chemical cell. The voltage generated varies with
the chemical concentrations and will decrease gradually from its peak
voltage until it is near chemically exhausted at which time there will
be a sharper drop. At exhaustion there will be chemical reaction
products that cause corrosion. The devices you use should be able to
operate at plus or minus 2 volts of the 9 volt nominal rating.
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