# Add Battery Test to a Multimeter

The photo shows an inexpensive (often free) multimeter from Harbor Freight. I added a white dot to the indicator. Notice that the white dot points to a battery test function for 1.5 volt and 9 volt batteries.

Batteries should normally be tested under a load because a no load voltage test could read normal, but drop considerably when the battery is under load. This multimeter's manual indicates that the battery test circuit adds 360 ohms of resistance as a load. According to the label on the meter, a 1.5 volt battery in good condition should show a current draw of 4 milliamps or more and a good 9 volt battery should show a current draw of 25 milliamps or more. There is nothing mysterious about this. It is a simple application of Ohm's Law, which says that voltage (E) in a direct current circuit is equal to resistance (R) multiplied by current (I), or E = IR. Factored, that is current (I) equals voltage (E) divided by resistance (R).
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## Step 1: No battery test function on your meter

This is not my better meter, but one I needed in a second location. It does not have a battery test function, but I decided it would be handy to add one. I can use the 200 m function. But, I will need to add about 360 ohms in resistance when in use. (My better meter also does not have a battery test function, and I made one of these resistor probes for it, too.)

How we can check the 48 V Lead Acid battery load with the help of load tester.

What does the 48 volt battery power? Can you measure the current flow in the circuit when its normal load is connected? Then you would use Ohm's Law to compare what the battery produces with what it should produce.

Otherwise, a standard battery test uses a carbon pile to handles.l of the current. Carbon pile testers are very expensive. Most you would find are likely to be for 12 volts. A tester for a 48 volt battery would be even heavier duty. I do not know where you would find one.

This is the best answer I know. I see you posted this question eleven times various places. Perhaps you could delete the other ten. Thank you.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

How we can check the 48 V Lead Acid battery load with the help of load tester.

pilm897 months ago

It wasn't mentioned but it's just as easy IMO to measure the voltage of the battery when loaded with a resistor, a dying AA battery might measure almost 1.5V with no load, but when loaded with a 150 ohm resistor for 10mA draw, the voltage may begin to collapse if the battery is weak. I prefer voltage simply because we already know what the nominal voltage for a 1.5V AA battery should be. Additionally one can choose the right resistor based on application, for example my digital camera that requires two AA batteries is labeled 0.6A at 3V, so I know each battery needs to be able to supply 0.3A, so a 5 ohm resistor loaded on the battery will quickly tell me if the battery can support this camera.

Phil B (author)  pilm894 months ago

Thank you for your comment and additional information. A voltage reading often tells all I need to know and works quite well.

imperiusPT8 months ago

This is great. Thanks for sharing.

Phil B (author)  imperiusPT8 months ago

I love practical, useful Instructables. Thank you for looking and commenting.

tutdude981 year ago
I ve got some 330 ohm resistor and if i put it serial to battery my reading should be 1.5/330 = 4.545ma?
Phil B (author)  tutdude981 year ago
That is correct, and 27 milliamperes at 9 volts.
Homepwner1 year ago
I really like this idea, I've read some of the comments and I think that with these types of batteries, absolute thresholds are not important. I just need to know if the battery is decent and this seems to be a good option.
Phil B (author)  Homepwner1 year ago
You make a very good point. In step 3 I mentioned, "It may well be that a battery considered depleted in one application would still function in a less demanding application." Over the years I usually tested a small home-use battery by taking a direct voltage reading with no load. There has usually been a fairly direct relationship between the remaining voltage and the depletion of the battery. In practice I quickly got to know at what voltage reading the battery would no longer do the job required for a specific application.

Perhaps we are all spoiled or deceived by the little battery testers with a red and a green zone on the indicator dial. We assume the battery is no longer useful if the needle falls slightly into the red part of the scale when it may still be useful for some applications. Somewhere I found a discussion that suggested testing a battery with a load resistance is truly useful only if the test resistance equals that of the actual circuit in which the battery will be used. Still, adding a resistance of 360 or 370 ohms is probably better than nothing, although I did actually test a 1.5 volt battery recently that showed the proper current flow with the test resistance, but a direct voltage reading showed a very depleted battery. I am not quite sure how that happened, but I have begun to check both the current flow under an artificial load and the voltage from a direct reading.

Thank you for looking and for commenting.
KellyCraig1 year ago
Thanks for the [two millionth] tip. Like you, I keep a few meters around (one in the shop, one in the van and one for the house). It would be nice to build probes for each that would stay with the meters.

I have some one inch square plastic tubes LED's came in and I might see if I can rig those to house the resistors or a small rheostat set to 360 and epoxied. The tubing would accommodate a label with values and a reminder of why it shouldn't be tossed ;)
Phil B (author)  KellyCraig1 year ago
Thank you for looking and for your comment. I encased resistors in a plastic soda straw because I wanted something thin I could hold against the side of the meter while I wrapped the test leads around it and the meter. Your square tubing should work well for you.
rimar20001 year ago
Phil, I measure directly Amps when testing batteries. I do that fast, to avoid discharging even more the battery.

If the current is near the max specified for that battery, I assume it is good. When it is discharged, amperes are very low, almost zero.
Phil B (author)  rimar20001 year ago
Osvaldo, that is a good idea if you know the amps capacity of a battery.
1 year ago
The batteries I use are these little 1.2 V, generally rechargeable. They always says their amperage.
The only problem doing that I suggest is the procedure discharges even more the battery. But if you are conscious on that situation, and are fast do measure, the problem is less important.
Phil B (author)  rimar20001 year ago
That helps me better to understand what you are doing.
technovative1 year ago
This is a good mod.
Phil B (author)  technovative1 year ago
Thanks. I wish I had thought of every aspect of it. I simply borrowed somethings others did and gave it a broader, more portable application.
MrOddjob1 year ago
As usual Phil, a very useful instructable. I have an ex British Telecom meter with battery condition function built in, but it is a fairly large chunk of meter to carry around. Three resistors and an alligator clip is a vast improvement. Thanks for sharing Phil, I know what I'll be doing tomorrow!
Phil B (author)  MrOddjob1 year ago
Thanks. I believe you could use a single resistor, maybe a 330 ohm or a 470 ohm resistor; or, you could use a small potentiometer you dial in to the resistance you want. The thresh hold current you are looking for would simply have different numbers. So, according to Ohm's Law, with a 330 ohm resistor the current would be 4.54 milliamps for 1.5 volt batteries and 27.2 milliamps for 9 volt batteries. With a 470 ohm resistor you would look for 3.2 milliamps on a 1.5 volt battery or 19.1 milliamps on a 9 volt battery. Life would be simpler if you could just go down to Radio Shack and buy resistors in almost any value, but I believe they square the value, double it, and the square root of that is the value of the next resistor. So, the next standard resistor from a 330 ohm resistor is a 470 ohm resistor (The square root of (330 x 330 x 2) equals 466.

Anyway, I hope you find it useful.