Checking battery charge using a multimeter?

[The Sauce]

My wife tends to leave batteries (among other things) lying all over the place - used, new...all mixed together. Can I use my multimeter to tell which batteries are good and, if so, can someone walk me through it?

 

[Shawn]

yeah. just set it to voltage.

 

[shortylickens]

Originally posted by: The Sauce
My wife tends to leave batteries (among other things) lying all over the place - used, new...all mixed together. Can I use my multimeter to tell which batteries are good and, if so, can someone walk me through it?

Put one probe on one end of the battery, the other probe on the other end.

If its alkaline it should measure 1.5 volts (sometimes a little more). 1 volt or less and it probably wont run your gadgets.

 

[yelo333]

I'm no EE, but here is how I understand it: Some multimeters have a battery test function on them. It measures the voltage while applying a small load. Testing just open circuit voltage without applying a load can yield bad results.

 

[The Sauce]

Ah thanks. I should have actually looked at my multimeter first. Didn't realize that they came with battery testing functions. Mine has settings for AA, AAA (1.5V), and 9V. Awesome.

 

[Eli]

Originally posted by: The Sauce
Ah thanks. I should have actually looked at my multimeter first. Didn't realize that they came with battery testing functions. Mine has settings for AA, AAA (1.5V), and 9V. Awesome.

That's handy.

Generally, you should test batteries with a small load.

 

[0roo0roo]

yea without load its going to give u useless readings.

 

[JohnCU]

how much of a load? you're already putting some load on it with the multimeter

 

[FeuerFrei]

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

 

[Eli]

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

 

[frostedflakes]

The ideal voltmeter has an infinite resistance. Obviously this isn't possible, but I think real ones do have pretty high resistances (on the order of megaohms). The idea is to put as little load on the device you're measuring as possible so that the reading you get is very close to the open circuit voltage.

 

[herm0016]

Originally posted by: frostedflakes
The ideal voltmeter has an infinite resistance. Obviously this isn't possible, but I think real ones do have pretty high resistances (on the order of megaohms). The idea is to put as little load on the device you're measuring so that the reading you get is very close to the open circuit voltage.

this.

i usually use 100 ohms or so (what ever is lying around near that value) to test batteries, a load on the battery means you are drawing some current from it. you check to see that the voltage drop with a current on it is not too much.

 

[JohnCU]

Originally posted by: Eli

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

so what do you suggest? i've never seen anyone measure a battery with resistor in the configuration.

 

[Eli]

Originally posted by: JohnCU

Originally posted by: Eli

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

so what do you suggest? i've never seen anyone measure a battery with resistor in the configuration.

Well, it's not necessary. It will still give you an idea of State of Charge. But it's better to apply a load and watch the voltage.

A brand new AA battery should read around 1.55V.

A dead one will read around 0.9-1.1V.

 

[futuristicmonkey]

Originally posted by: Eli

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

For those dmm's which cost like $2.00, yes. Even the Canadian Tire Mastercraft dmm's have 1 megohm input impedance.

 

[KK]

If you need to place a load on a battery before reading the voltage, just get a piece of straight wire and connect each side to each end of the battery. Then you should be able to get an accurate reading.

 

[herm0016]

Originally posted by: KK
If you need to place a load on a battery before reading the voltage, just get a piece of straight wire and connect each side to each end of the battery. Then you should be able to get an accurate reading.

load=/= short circuit.
this is a good way to make a battery "pop" open, and to ruin it.

 

[JohnCU]

Originally posted by: herm0016

Originally posted by: KK
If you need to place a load on a battery before reading the voltage, just get a piece of straight wire and connect each side to each end of the battery. Then you should be able to get an accurate reading.

load=/= short circuit.
this is a good way to make a battery "pop" open, and to ruin it.

actually that is a hell of a load on the battery having to generate that much current. i think he was being sarcastic anyway.

 

[frostedflakes]

Yeah, that's not a good idea, heh. I doubt alkalines will explode or anything like when you short-circuit car batteries, but as herm mentioned it would probably damage the battery. The wire will also get very hot and could cause burns.

 

[FeuerFrei]

Originally posted by: Eli

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

And by 'load' I mean 'resistance.' erg

Adding resistor in series with the battery & voltmeter will just mess up the voltage reading. It'll read low.

 

[JohnCU]

Originally posted by: FeuerFrei

Originally posted by: Eli

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

And by 'load' I mean 'resistance.' erg

Adding resistor in series with the battery & voltmeter will just mess up the voltage reading. It'll read low.

nah they mean put a resistor across the battery and then measure the battery as it is supplying power to the resistor.

 

[DrPizza]

then wrap the wire around a nail a dozen times before connecting it to both ends of the battery. Your battery will be just fine for those 3 seconds it takes to measure the voltage.

But, it shouldn't be necessary for doing a quick check of which batteries are good and which are shot.

 

[JohnCU]

for my own fun i just measured a battery open circuit and short circuited (AAA)

open = 1.59V
shorted = 0.59V

 

[herm0016]

Originally posted by: DrPizza
then wrap the wire around a nail a dozen times before connecting it to both ends of the battery. Your battery will be just fine for those 3 seconds it takes to measure the voltage.

But, it shouldn't be necessary for doing a quick check of which batteries are good and which are shot.

hmm.. an inductor. that would work fine as long as its quick.

 

[Eli]

Originally posted by: futuristicmonkey

Originally posted by: Eli

Originally posted by: FeuerFrei

Originally posted by: JohnCU
how much of a load? you're already putting some load on it with the multimeter

Really. The multimeter should provide the load. <_<

lol

The typical load in the Voltage circuit of a multimeter is 10,000 Ohms.

For those dmm's which cost like $2.00, yes. Even the Canadian Tire Mastercraft dmm's have 1 megohm input impedance.

Ah, yeah. You're right.