Measuring MAX current of a battery 9 volts, AAA, AA

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danny davis

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This DVM meter measure the battery current and loading the battery

9 volts is at 25 mA , is 25mA the max current out of a 9 volt battery?
1.5 volts is 4.0mA , is 4.0mA the max current out of a 1.5 volt battery?

Why are they testing a 9 volt batterys current output at 25ma?
Why are they testing a 1.5 volt battery current output at 4.0mA?

When I measure a batterys voltage or current , i Use a 10 ohm resistor across the battery to load it

If i use a 2 ohms resistor i have to use a 5 watt resistor

But how do you find out the max current out of a battery?

Do you have to print out the datasheets to know what the max current out of a battery is? 9 volt, AA, AAA, D cell?

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Here is the DVM meter that measures batterys
http://www.harborfreight.com/household/electrical/7-function-multimeter-98025.html
 

See the datasheet of 9V battery

https://data.energizer.com/PDFs/522.pdf

Battery storage capacity is mentioned in mAh, it means how much current drawn from a battery within one hour at rated voltage. In the data sheet showing 600mAh, It means you can drawn 600mA current for one hour at 9V (Practically it is not possible, you can drawn 50% to 60% stored charge at maximum current). Other wise you can draw 25mA for 24 hours at rated voltage


9 volts is at 25 mA , is 25mA the max current out of a 9 volt battery?

No, 25mA is the safe current for maximum efficiency of the battery.

1.5 volts is 4.0mA , is 4.0mA the max current out of a 1.5 volt battery?

No, 4mA is the safe current for maximum efficiency of the battery.

Why are they testing a 9 volt batterys current output at 25ma?

25mA current drawn will give maximum time of discharge, so we can find out the battery life.

Why are they testing a 1.5 volt battery current output at 4.0mA?

4mA current drawn will give maximum time of discharge, so we can find out the battery life.
 

But how do you find out the max current out of a battery?
Click to expand...

Maximum current is determined by internal resistance.

There are many types of battery chemistry. They have different internal resistances.

You can get a general idea from the mA-hr rating printed on some batteries (although this not synonymous with maximum current).

Example, rechargeable types of nicad and NIMH. I have some old AA nicads which are 720 mA-Hrs. They have declined with age.

Today's AA rechargeables deliver 2500 mA-Hrs. Their internal resistance is much lower.
 

The standard way of measuring the "goodness" of the large 1.5 dry battery (D cell or U2) is to switch your AVO to 10 A DC and flash it across the battery connections, a good battery will give a current over 8A.
So good batteries will give a very high peak current compared with their nominal rating.
Frank
 


1.) the safe current for maximum efficiency of the battery? how do u find out what the safe current is?

So The DVM meter is loading the battery at 25mA , and the other setting it's loading the Battery at 4.0mA?

25mA current drawn will give maximum time of discharge, so we can find out the battery life.
Click to expand...

How do you know the maximum time of discharge? how is 25mA going to be the battery life? or 4.0mA is the battery lifes? who comes up with those current figures for the battery life and time of discharge?

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There are many types of battery chemistry. They have different internal resistances.
Click to expand...

So I measure the OHMS with my DVM across the battery's terminals to measure the internal resistance of the battery?

or how do you measure the internal resistance of a battery?
 

danny davis said:
is 25mA the max current out of a 9 volt battery?
Click to expand...
The datasheet for the alkaline 9V battery shows MORE THAN 350mA for one hour when the battery voltage has dropped to 4.8V.
The datasheet for a Lithium 9V battery shows MORE THAN 500mA for 1.2 hours when the battery voltage has dropped to 6.8V.
The datasheet for a Carbon-Zinc 9V battery shows MORE THAN 150mA for 6 minutes when the voltage has dropped to 4.8V.
you can lookup a Super Heavy Duty 9V battery yourself.
Why didn't you know that there are 4 different kinds of 9V disposable batteries?
Did you know that there are at least 2 different kinds of rechargeable 9V batteries?

is 4.0mA the max current out of a 1.5 volt battery?
Click to expand...
1.5V batteries can be low current hearing aid batteries or sizes AAAA, AAA, A, N, C and D. Most also have 4 kinds of disposable and there are at least 2 different kinds of rechargeable batteries in some of those sizes.
Don't you think a tiny hearing aid battery cannot provide the high current of a D cell?
Don't you think Lithium or Alkaline can provide much more current for a much longer time than Carbon-Zinc?
 
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A good one draws 8A and an old one draws 200mA.
Click to expand...

A battery doesn't DRAW current , it outputs current
Something that draws current is a circuit or component to make it turn on and operate

Why u measuring the current , when the voltage is proportional to eachother , if voltage drops so does the current

So if the battery is 9 volts , why u measuring the current? just measure the 9 volts and apply a load until the 9 volts drops to 8 volts u have found your load value

10 ohms across a 9 volt better is a large load and a weak 9 volt battery will discharge really fast , a good 9 volt battery with a 10 ohm load will stay at 9 volts

The Cheap Chinese meter measures batteries at low currents because they might be cheap Chinese batteries that spent a few months on a boat then a few years leaking on a shelf at The Dollar Store.
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Why are they measuring batteries at 25mA and 4.0mA? why does currents and for what reason?

I tried to measure the test voltage on the Battery setting mode on the DVM meter, one is for 9 volts and the other is for 1.5 volt battery test

I got NO test voltage output from the DVM meter in the battery test for either the 9 volt and 1.5 volt

So the DVM meter is not outputting a test voltage, it must be a resistance load or something

I measured the resistance it's at 1K ohm when the DVM meter is in battery test for either 9 volts or 1.5 volts , so it's testing the battery with a 1K ohm load it seems
 

danny davis said:
just measure the 9 volts and apply a load until the 9 volts drops to 8 volts u have found your load value
Click to expand...

This is an ideal approach. A load is the way to properly test a battery.

However variable loads (or rheostats) are inconvenient. And a plain potentiometer is liable to burn up.

So it more practical to use a fixed resistor for the test load.

Why are they measuring batteries at 25mA and 4.0mA? why does currents and for what reason?
Click to expand...

I can picture 25 mA being a sensible load for a 9V battery, but as for 4 mA, that seems like too light a load to take a sensible reading of a battery.

I have a Radio Shack battery tester which puts 150 ohms across 1.5V batteries.

For a 9V, it uses a higher ohm value. A 9V battery consists of 6 or 7 or 8 cells which are much smaller than a AAA cell. It is depleted quickly if we draw high current from it.
 

danny davis said:
A battery doesn't DRAW current , it outputs current
Click to expand...
Correction: I used my current meter to draw 8A from a good AA Ni-MH cell.

Why u measuring the current , when the voltage is proportional to eachother , if voltage drops so does the current
Click to expand...
Because I use AA Ni-MH cells at high current running motors and heaters. When a cell is worn out then it cannot produce high current.

IT WILL NOT STAY AT 9V. You are killing a little 9V battery with a current of 9V/10 Ohms= 900mA.

Look at the Duracell datasheet for their 9V alkaline battery. It performs poorly with a load current as high as 250mA. It has an internal impedance of 1.7 ohms so it begins producing 8V when its load is 588mA. With your load of 900mA it is dead in seconds.

Why are they measuring batteries at 25mA and 4.0mA?
Click to expand...
When its voltage drops to 7V a Duracell 9V alkaline battery lasts for 50 hours at 10mA and for 7 hours at 50mA. At 25mA it might last for 10 hours.
A very quick test of its voltage at 25mA will not use up much of its life.
A current of only 4mA at 1.5V is for testing a small battery cell.

The meter is defective or you do not know how to use it.
Why do you think the meter should OUTPUT a test voltage when it is loading a battery and displaying its voltage??

I measured the resistance it's at 1K ohm when the DVM meter is in battery test for either 9 volts or 1.5 volts , so it's testing the battery with a 1K ohm load it seems
Click to expand...
Ohm's law says the current is 9V/1k= 9mA and 1.5V/1k= 1.5mA.
I think the 1.5mA at 1.5V is for testing a tiny hearing aid battery.

danny davis said:
How do you know the maximum time of discharge?
Click to expand...
You simply look at the datasheet for the battery.

So I measure the OHMS with my DVM across the battery's terminals to measure the internal resistance of the battery?
Click to expand...
ABSOLUTELY NOT!
You must NEVER connect your ohm-meter to a voltage source.
Use Ohm's Law to calculate the internal resistance of a battery after loading it and measuring its voltage.
 

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Why u measuring the current , when the voltage is proportional to eachother , if voltage drops so does the current
Because I use AA Ni-MH cells at high current running motors and heaters. When a cell is worn out then it cannot produce high current.
Click to expand...

But can't you just measuring the voltage and if the voltage drop then you will know if a CELL is worn out? because voltage is proportional to current?


So how do you find the RIGHT load resistor to put in parallel to LOAD the battery to test the LIFE and max Current?


So it's a useless test? it does nothing? to measure a battery at 25mA?

What is the 25mA or 10mA current called? what kind of current test is this called? a load current battery test?

Does a LOAD resistor VALUE in parallel determine this load current battery test at 25mA , 10mA? how does the meter internally get this 25mA , 10mA current test?
is it just a LOAD resistor in parallel to the battery terminals?

The meter is defective or you do not know how to use it.
Why do you think the meter should OUTPUT a test voltage when it is loading a battery and displaying its voltage??
Click to expand...

The Measured the output probes on the battery test, it measured 1K ohm , so what is going on internally inside the DVM meter in battery test check mode?


So what equipment can test the internal resistance of a battery? the ESR ?
 

danny davis said:
But can't you just measuring the voltage and if the voltage drop then you will know if a CELL is worn out? because voltage is proportional to current?
Click to expand...
No because a new cell and a worn out cell both produce the same voltage. The worn out cell has a high internal resistance which reduces the voltage output when there is a load and it limits the maximum output current.

So how do you find the RIGHT load resistor to put in parallel to LOAD the battery to test the LIFE and max Current?
Click to expand...
I simply SHORTED my Ni-MH cell because it is rechargeable then I re-charge it. I would NEVER short a disposable battery because it would kill it.
A 9V alkaline battery is shown on its datasheet to produce 25mA for about 10 hours when the voltage has dropped to 7V so 25mA is a pretty good test if tested for a short duration. The resistor is 9V/25mA=360 ohms.

So it's a useless test? it does nothing? to measure a battery at 25mA?
Click to expand...
It is a good test that shows the battery voltage at the current that is normally used. Nobody overloads a little 9V battery.

What is the 25mA or 10mA current called? what kind of current test is this called? a load current battery test?
Click to expand...
Call it anything you want.

Does a LOAD resistor VALUE in parallel determine this load current battery test at 25mA , 10mA? how does the meter internally get this 25mA , 10mA current test?
is it just a LOAD resistor in parallel to the battery terminals?
Click to expand...
The meter simply measure the voltage of the loaded battery. The 25mA flows from the 9V battery through the resistor.

The Measured the output probes on the battery test, it measured 1K ohm , so what is going on internally inside the DVM meter in battery test check mode?
Click to expand...
You are lucky that your Fluke meter is idiot-proof. You must NEVER measure ohms when there is a voltage present.

So what equipment can test the internal resistance of a battery?
Click to expand...
Use a load resistor, a DC voltmeter and Ohm's Law.
Why do you need to know the internal resistance of a battery? Simply load it and measure its voltage. If its voltage is too low then replace the battery.
Oh, you want to cut open the battery and fix it??
 

The meter simply measure the voltage of the loaded battery. The 25mA flows from the 9V battery through the resistor.
Click to expand...

How did they come up with the 25mA, isn't the resistor value in parallel set the current value to be at 25mA? or what kind of circuit do they use to get the 25mA?

A 9V alkaline battery is shown on its datasheet to produce 25mA for about 10 hours when the voltage has dropped to 7V so 25mA is a pretty good test if tested for a short duration. The resistor is 9V/25mA=360 ohms
Click to expand...
.

I still don't get why use use 25mA to test a battery and why it's a good test

I would think loading the battery to the MAX to see what's it's max, current output would be at the rated voltage

Rated voltage is 9 volt battery
Testing a battery at 25mA would take 10 hours before u saw any voltage drop , how is that a good test?

Rated voltage is 9 volt battery
You want to load the battery to the max so see how much current it's still have inside the battery and how much current it's going to output at that voltage of 9 volts
 

9V batteries are practical in devices that drain slight current, or infrequent current. (Unless you have a drawerful of them.)

If you need more power then you might as well upgrade to larger batteries.

danny davis said:
I would think loading the battery to the MAX to see what's it's max, current output would be at the rated voltage
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Current you drain from the battery (non-rechargeables) reduces its lifespan. Draw more current, the shorter it lasts. So why do a severe test on a 9V?

If any one of those 6 cells gets drained prematurely, you cannot get 9V from it.

You can measure its voltage to get a rough idea how much life it has. This is not accurate in all cases. Nowadays a new alkaline measures 9.6V. And I've seen 9V's that produce 9V but cause smoke detectors to beep a low-V alert.
 

've seen 9V's that produce 9V but cause smoke detectors to beep a low-V alert.
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This is my point, it measures 9 volts, but how much current is inside the battery? its a weak battery even tho it measures 9 volts it has microamps of current that's why it's causing the smoke detector to keep because the battery Not loaded measures 9 volts but when the 9 volt battery is loaded or a circuit is drawing current from it , it the voltage discharges down

I always measure a battery while it's IN CIRCUIT , so you measure the battery of it under a circuit load plus the circuit's current draw
 

A battery does not 'hold' or 'store' current. It is a chemical reservoir which releases current on demand. How much it can release depends on the rate the chemical reaction can take place.

At risk of another million questions from you, I will try to explain how we MODEL the performance of a battery:

As you have already noticed, the voltage from a discharged battery may still be high, what changed when it discharged was it's ability to maintain that voltage when current was drawn from it. The real reason is that the chemicals within the battery have exhausted their ability to react quickly, but they can still react slowly. They can bring the voltage up to normal (or near normal) but not keep it there under load.

Trying to do the complex chemical math to work out how much current could be produced would be a near impossible task so we do it a much simpler way. We IMAGINE the battery is perfect but it has a resistor in series with it. I stress this is NOT a physical component, there is no resistor inside the battery packaging, it is just a concept that produces a close approximation to how a real battery works. According to Ohms law, when a current passes through a resistance, a voltage is dropped across it. Likewise, the voltage across a battery drops when current is drawn from it. So the model of a perfect battery with a resistance is series with it shows the same effect, more current = less voltage.

We call this imaginary resistor the batteries "internal resistance" for obvious reasons. On a new battery the resistance appears to be low and as it ages or discharges the resistance appears to increase. Again, according to Ohms law, the higher the resistance the more voltage per mA will be dropped across it. So a new 9V battery would have a low resistance and measuring the voltage across the terminals, bearing in mind the meter draws negligible current, would be 9V. Measuring an old and discharged 9V battery, while drawing negligible current will also drop almost nothing across the internal resistance so it might still say 9V. The difference comes when you try to draw more current, the output voltage approximates to "(perfect battery voltage) - (internal resistance * current being drawn)" so as the internal resistance increases, the voltage proportionately decreases.
Again, I stress the internal resistance is really a reluctance of the chemicals to react, it is not a physical component.

As for why different currents are specified, let me quote two extremes,
1. would it be sensible to measure a car battery discharge time at 1mA load?
2. would it be sensible to measure a watch battery discharge at 10A?

In case 1, 1mA is insignificant to a battery that might be rated at 100AH and even differences in one battery to the next on the same production line would make more difference than the 1mA load.
In case 2, the battery would be incapable of delivering anything like as much as 10A so even a theoretical calculation like "0.05 seconds" would be meaningless.

Accordingly, the test currents are set to be useful in terms of typical battery usage. My car battery for example is rated at 80AH and 275A for 10 seconds, my watch battery is probably rated at 100uA for 1000 hours.

Brian.
 

Measuring an old and discharged 9V battery, while drawing negligible current will also drop almost nothing across the internal resistance so it might still say 9V.
Click to expand...

Why would it still measure 9 volts? this is under no load right? but when there is a load the voltage drops

What is going on inside the battery to measure 9 volts still at no load? is it the internal resistor got larger in value? but why is the voltage the same at 9 volts?

I have seen a lot of batteries like this

the test currents are set to be useful in terms of typical battery usage
Click to expand...

So what you're saying is a DVM meter that has a test current at 25mA for a 9 volt battery is a very common typical current draw current for most circuits that run on a 9 volt battery? most circuit draw 25mA for a 9 volt battery?
 

I can't understand why you say you are eager to understand electronics yet you seem to be incapable of reading messages on here.

I explained in detail about the internal resistance. Start with Ohms law and work out how much voltage is dropped across ANY resistance when no current is flowing through it. Then consider how much current a typical DVM draws when measuring voltages.

If your DVM is drawing 25mA on any voltage range, I suggest you throw it out and buy a decent one.

Brian.
 

If your DVM is drawing 25mA on any voltage range, I suggest you throw it out and buy a decent one.
Click to expand...

No only in battery tester mode it is

I explained in detail about the internal resistance
Click to expand...

When the internal resistance is LOW and you measure the battery voltage with NO LOAD = 9 volts
When the internal resistance is LARGE and you measure the battery voltage with NO LOAD = 9 volts

How does the internal resistance get from being low value to a large value? what makes it grow in value?

When the internal resistance is low on a brand new battery, how do you measure the MAX current draw output? with what value resistor?

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My manager makes me test batteries using a 10 Ohm resistor , for AA, AAA, 9 volt batterys , D cells, etc. , what do you guys use?

I don't understand how 25mA current test the battery , tells the technician if the internal resistance is a low value or a LARGE value, how do you know?
 

As we told you many times, 25mA is a normal load for a 9V battery. It has 6 tiny AAAA cells in series inside. A 10 ohm load will kill it in seconds.
Maybe a 10 ohm load can be used for a much larger alkaline D cell that has 24 TIMES the capacity of a 9V battery.
Your manager is CRAZY to kill a little 9V battery with a 10 ohms load.

As I showed on the datasheet, a 50mA load on a 9V alkaline battery shows its voltage drop (caused by its internal resistance) pretty well when it is depleted. A 25mA load is almost the same.
 

Why you guys call the test current a LOAD? the 25mA is a load? it's a current draw

So a current draw= a LOAD?

What value resistor would u use for a 9 volt battery than?
 

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