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Check battery w/ Multimeter?

  • Thread starter Thread starter mortation
  • Start date Start date
M

mortation

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Is it possible to check a battery with a multimeter? I think you can get a current reading if there is a charge but I don't remember the specifics off the top of my head.
 
IME, no. I have had batteries that would have a good voltage reading but be bad. I think the only way to do it with a DVM is to put a load on the battery and look at the discharge rate.
 
mortation said:
Is it possible to check a battery with a multimeter? I think you can get a current reading if there is a charge but I don't remember the specifics off the top of my head.
Click to expand...

As lecroy said, you can't really get a definative answer, but the following will turn up a battery that is definately shot.

Charge with a charger until definately fully charged.

Take off charger and check voltage at no load, if less than 12.5 its shot.

Turn on the head-light, wait 30 seconds and check voltage at battery terminals, if less than 10 its shot, less than 11 is suspect but may be ok.

Leave headlight on for 2-5 minutes, a significant drop ( say more than 1 additional volt) is probably shot.

recharge fully

There are more specific and extensive tests at
http://www.batteryfaq.org/
 
mortation said:
Is it possible to check a battery with a multimeter? I think you can get a current reading if there is a charge but I don't remember the specifics off the top of my head.
Click to expand...

The short answer to your question is yes...........the basic idea behind load testing an automotive (bikes etc) cranking battery is that it should crank the engine for up to 15 seconds without the terminal voltage dropping below 9.6 volts - this allows for a significant attempt at starting while allowing the ignition system enough to operate. With that in mind you can check to see if your battery is "good enough" for your engine using that criteria.

The longer answer is no as it requires a load test, in addition to the voltage your multimeter will read. If you have can find either the CCA (cold crank ampere) rating of your battery or it's AH (ampere-hour) rating AND you have access to (or obtain) a battery load tester (or make one) you can test your battery with respect to it's original rating by doing the following: Knowing the CCA rating of the battery - apply a load of 1/2 the CCA rating for 15 seconds and, at room temperature, see that the terminal voltage doesn't drop below 9.6 volts at the end. Knowing the AH rating, apply a load of 3x this for 15 seconds with the same result.
For example......the battery for my 79 GS1000 is a YB14L-A2 and INTERSTATE rates their version (they tell me it's a rebadged YUASA) at 190 CCA. I apply a 95 ampere load for 15 seconds with my adjustable load tester and find the terminal voltage at this time of 10.5 volts.....an easy pass.

Hope this makes sense or at least doesn't confuse you more ;)
 
I would just add that putting a 95 amp load on a questionable battery for any length of time is a questionable idea. If you're going to do so, do it in a trash can or the like.
 
smagnusen said:
I would just add that putting a 95 amp load on a questionable battery for any length of time is a questionable idea. If you're going to do so, do it in a trash can or the like.
Click to expand...

This isn't a questionable idea at all and represents one example of a standard load test. That the battery may or may not fail lets you know where the battery is with respect to its designed spec. Having said that, I've often tested batteries which didn't pass........and then retested at a progressively lower rate (sometimes this requires recharging) to be able to re-rate a battery for suitability. And just to add; typically a battery that will pass a load test at spec, will be able to a couple of times in short succession.
 
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