How to Check AA/AAA Alkaline Battery Using a Voltmeter

We all run into a situation when batteries in our remotes, toys, keyboards/mice run out. If we don't know how to check a battery we might throw out a perfectly fine battery (especially when we have a pile of them somewhere in the drawer).  

This electronics tip has to deal with checking common alkaline AA/AAA batteries or AA/AAA rechargeable batteries for proper voltage with a voltmeter.

Disclaimer : some people might say that a battery should always be tested under load but I have found that in most common household applications this is insignificant and will not change the results of the testing too much. 

Things that you will need :
+ Voltmeter
+ Alkaline battery

Basic facts : 
The proper voltage for AA/AAA alkaline battery is 1.5V
The proper voltage for AA/AAA NiCd/NiMh rechargeable battery is 1.25 Volts

To test the battery, turn on your voltmeter, put the voltmeter on DCV and make sure that it is far above the battery voltage, on most voltmeters there is a setting "20" in the DCV area, so switch your voltmeter to that setting. 

With the battery in front of you, put the red probe to battery's nipple (+) and the black probe to the battery's flat side (-). Notice the voltage reading on the voltmeter.

If the reading is more than 1.3V for alkaline battery (not rechargeable battery) then the battery still has some juice left in it, don't throw it away. Otherwise, properly discard of the battery.

Tip : do not use old and new batteries in the same device at the same time. Try to use batteries that have same amount of energy stored in them. 

Another tip: I sort my batteries according to Voltages, 1.35+ Good, 1.2V-1.3V Ok (but almost out), 1V-1.2V Discard.

I will attach some pictures of measurements in action. 

Instructions on how to use a multimeter are out of scope of this Instructable, you can find some information here: http://www.ladyada.net/learn/multimeter/

Comments

[Reluctant Poster]

Today I had a major name-brand digital thermostat fail, driving my house temperature to 80° before the failure was caught, wasting a lot of expensive energy as well. The thermostat is battery powered, and when checking the two AA’s it uses, the voltage on each was 1.32 and 1.33V, respectively. in some cases, that voltage may be usable, but in this application it was insufficient to power the relay that shuts off the furnace. Just be very careful of your particular application.

[jakeoclubs]

Was you furnace stuck "on" when the cells failed?

[noneYettookmyUN]

This is not a totally foolproof way to check cells, and you are certainly right to advise folks to be thoughtful and prudent about where they put their faith. Obviously I haven't personally examined your home climate control system, so I'd be a fool to spout off and tell you there's been a mistake. But I have to say that something seems amiss here.

I don't mean to insult your intelligence, and if you know your stuff and are certain about what happened, please forgive me. But in case you're not too familiar with HVAC and are just guessing, I want to give you a heads-up that the problem could be something else and you may want to be on the lookout. Although it appeared a "low battery" was your problem, it could be that the fresh battery, (or the some aspect of the battery change) just masked or reset a different problem.

I am not an HVAC pro or guru; my observations are not definitive. Prelude over. There are two things that seem unusual to me, and here's what I can tell you. Although electronic thermostats do (usually, anyway) rely on their own power source to run their internals (including a switch that determines whether the furnace will be told to run), the actual messenger that switches it on is typically a ~5V line which is supplied by a transformer in the furnace. The thermostat's power just has to decide to close a little circuit on its board, which doesn't usually take much juice. Granted, that doesn't prove anything. The thing that bugs me more is thatit's usually a closed circuit that turns a unit on. Lack of power should result in a unit that fails to turn on.

I won't pretend that I can tell you what else could have been at fault for the "stuck on" condition, or even that I know for certain it wasn't just as you said. I just wanted to help out by telling you that from here it looks like there might be another problem lurking. If you know something I don't, I'd be happy to have you educate me.

Thanks, or you're welcome. Or both.

[ru4him]

I have also experienced a brand name thermostat with low batteries that caused my furnace to fault in the on state on two occasions. The manufacturer heard from me, and they admitted to a problem and sent me a new model of thermostat. So while I agree it SHOULD fault in the off state... that's not always the case. I was surprised too! I think it was a 3M thermostat...

[RourkeM]

"Tip : do not use old and new batt..." I hear that tip all the time, but have never once seen an explanation accompany it. I think it is an oft repeated, unsubstantiated tidbit that is as helpful as the tip, wait 30 minutes after eating before swimming. I've had to use old and new on countless occasions and regularly eat a whole turkey before during and after my swim and have yet to see any detrimental effects if you can overlook an abundance of glow in the dark turkey farts.

[am27wYOC79l7uDMd]

If old and new batteries are similar voltage it’s no big deal. If old has 1/2 capacity of new they’ll simply equalize and you’ll lose some capacity from the new battery. Again no big deal. It’s only $.

[gary.barker]

If the voltages are to different then you'll drive a reverse current through the week battery and it could fail physically. It's pretty unlikely but not worth the risk

[krazyinktattoos]

I quit literally had a battery explode inches from my face a few days ago. Thankfully the battery acid stayed contained and I wasn't injured. Could it have been the 2 brand new batteries I put in with the 2 very old batteries? Like most, I've heard not to mix old and new but didn't think about it possibly causing batteries to burst. What I found most odd about the whole experience was that the light in which the batteries were installed stayed on for a good 15-20 min after the battery explode. In fact, I had to turn the light off. Anyone know if that's normal?

[bdannh1]

The other day i needed to check the voltage in a couple of AA batteries. I plugged the cables into my analog multimeter and touched the leads to the ends of the batteries and measured the voltage. When i finished i was putting everything back in the box and noticed i had forgotten to put the batteries in the multimeter but it still worked. Doesn't the meter need batteries to check voltage?

[philnjune67]

Analog meters use power from the battery being tested to swing the needle. Digital testers require an internal battery to work

[moosetooth]

I believe the battery in a multi meter are necessary for ohm function. It sends a small current through the circuit to measure resistance. Also necessary for continuity checks.

[DavidP236]

With the multimeter in the photo you can test unloaded and loaded. The battery test (loaded) position is at the upper right on the dial in the 1:00 position. Set to this, put the red lead in the middle hole and the black in the bottom. You should read 4.0 mA (milliamp) for a AA or AAA battery.

[mlah]

To those who stumble upon this, this is why you need to test the battery under load. The voltage of an unloaded battery will not change significantly as it dies. A fresh battery and a dead one will both show similar voltages unloaded.

[johnlax27]

I think he is talking about testing for voltage while the battery is under load. You're talking about amperage--two different things.

[askjerry]

I'd like to offer a few corrections, additions, and pointers.

Testing a battery with a multimeter will only tell you what the voltage of an UNLOADED cell is. In other words... you could have two batteries that read with an identical reading of voltage... but when you connect them to a load... let's say a motor... one will spin niely and the other will fail... run slow or stall.

Why? Because the CAPACITY of the failed battery has diminished. Let's take the example of a AA battery... if it has a 2000mAh capacity, that means that it can support a load of 2000 mA for 1 hour... or 1000 mA for 2 hours. This means that if you were running a toy that drew about 200 mA... it would run for 2000mAh/200mA or 10 hours.

So how do you check the battery? Under a load. Let's use the example above... we don't want to draw 2000mA on the battery... that's a huge load all at once. But instead... let's draw 1/10 of it's capacity... 200mA. We can take the voltage 1.5 volts / 0.2 amps (200mA = 0.2A) and get 7.5 ohms. So if we find an 8 ohm resistor and put it across the battery... it should still be close to 1.5v... but if it drops way down... to less than a volt for example... then it is likely discharged or going bad.

Another issue with the 1.5 volt battery... a NON-RECHARGABLE battery is rated for 1.5v fully charged. but... a NiCad battery is rated for 1.2V FULLY CHARGED. And I believe a lipo is like 1.25V if memory serves me.

I actually use this fact in my projects... an Atmel runs 3.0v to 5.5v...

4 AA batteries.... at 1.5v = 6.0v which would be high for my 5v Atmel processor...
4 AA batteries.... at 1.2V = 4.8v which is just fine.

I hope that helps.
Jerry

[SteveR46]

The article was pretty clear that this was for testing an alkaline AA or AAA. Also, the test is for determining whether the cell was depleted or not, not whether it had malfunctioned. If the cell tests fresh under no load, but drops below 1.2 v under load, you are either overloading the battery, or the battery is defective (or both)

[XgudwilX]

thank you. common sense.

[MichaelW328]

I know this comment is 6 months old, but I am going to reply any way in case someone reads this later.

As askjerry indicated, testing a battery (of any chemistry) unloaded is pretty much a useless endeavor. The ONLY way to test a battery is to estimate the current draw scenario, and 200mA is a good base case scenario, and test it with an equivalent load. When you test a battery unloaded you can get nearly the full "new" voltage on a battery with very little capacity left. Just use a 1/2 watt (or greater) resistor as a load and you can get a true estimate of whether the battery is good or bad.

[iptest0125]

Hi, is the resistance going to make any difference during the test? For example I have couple 50 ohms laying around, which should draw a much less current, will it show different result from 8 ohms?

[SteveR46]

My multimeter has a simple bat test mode. For 1.5v it measures the voltage under a 100mA load.

To the point...Does testing the battery under load really matter? No, not for most electronic devices. It might matter a little bit if it runs a motor, or perhaps a flashlight. Still, we are talking about deciding whether to dispose of an inexpensive battery or to replace it with a new one. I see no need to overthink this and go searching for load resistors. If in doubt-throw it out!