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How to test a car battery?

This could be an another thread from harbor freight…
I have got this cheap 7 function multimeter from hf. Reading the instruction manual (who a heck does that any more?) it says do not use on automotive batteries.
Any reason for this or is there a way to check the state of the battery with it? And if there is one, then how would you do it?

Set that thing to read DC voltage in the 20V range and put the leads in the appropriate holes. Put it across the battery.
With the engine off, you’ll read around 12V.
With the engine running, you’ll likely read around 14.4V

A true battery test is a load test. You can’t do that with a simple multimeter.

As Remco stated, your little $5 meter can indeed measure the battery and charging systems voltage…

If you want to test the battery for serviceability, H.F. sells a decent battery load tester that will reveal a weak battery in short order…

I have used a cheap multimeter to get a rough measurement of the health of a battery by noting the voltage with no load on the battery and then noting the voltage drop when I have somenone crank the engine over with the starter. It isn’t as good as a load test, but it works for me.

Most auto parts stores will test your automotive battery for free, so why not let them do it? They’ll bring the machine out to your car, so you don’t need to remove the battery to bring it into the store.

I was hoping this would be a different type of thread. I had a motorcycle battery completely fail on me. It just went from working to completely dead. Since I couldn’t find my circuit test light, I had to get creative. I unhooked the motorcycle battery and connected the motorcycle to my car battery with a pair of jumper cables. When it started right up, I realized I needed a new battery.

Yes, you need to do a load test; a small meter will only reveal if you have a bad cell.

Batteries are rated for cold cranking amps as well as reserve capacity. Any shop can do this in minutes.

Most auto parts stores will test a battery for free, a multimeter does not cut it in my book. As @Docnick says you need to measure cranking amps, not voltage.

As stated above a battery should register about 12.8v with the engine off and system voltage should stabilize at about 14v with the engine idling and no major accessories operating. If the voltage remains above 11v while the engine is being cranked for several seconds it is usually adequate. A $5.00 gauge from Harbor Freight or a dollar store should be able to tell you all you need to know. A VAT 28 or a VAT 40 are much quicker but where would you keep one and they cost many hundreds of dollars years ago. Does anyone know what Sun/Snap-On offers in the Volt-Amp-Tester with a carbon pile these days.

@Rod Knox, last I looked a decent carbon pile electrical system tester was in the $1000-$1500 range.

How to test a car battery?

What, you too fancy for the tongue test any more?

What you don’t want to do with this VOM is use the amp scales on a car battery. If you do that, all the smoke stored inside will immediately escape and without the smoke, the meter won’t work anymore.

I concur the best way to test a battery is let one of the auto parts store or retail auto repair places do it. Most of them will test the battery and charging system for free.

When I buy a new battery, after it’s fully charged from a few weeks of normal driving, one thing I do to calibrate the battery condition is turn the engine off, and measure the battery voltage when everything is off, and again when the headlights are on bright. The voltage will be lower when the headlights are on, as they put a significant current load on the battery. I record those two numbers for future reference. As the battery ages, the voltage when everything is off doesn’t change much, but there’s a significant drop when the headlights are on bright with an aged battery.

There is normally little need to worry about a car battery. Keep jumper cables in the trunk and when you need them and if the battery is past the warranty it may be new battery time. Car batteries are cheap; 70 bucks for 5 years is only $14 per year.

You should test the battery after it’s been on a charger for a while. A good battery should show 12.6 volts on your VOM. Six cells X 2.1 volts per…

You can do a simple test by disabling the engine so it won’t start. (Fuel pump relay removed, etc)
Attach the VOM leads to ground and a battery voltage source and place the VOM on the dash or windshield where it’s visible.
Crank the engine for 10 to 15 seconds and watch the voltage. It should not drop below 10.2 at a bare bones minimum after that period of time. If it hits 10ish or so the battery is getting iffy and down around 9ish means you need a battery.

Thank you for all the replies.
Being on the creative side @whitey this is actually a truck battery mounted on an industrial size woodchipper. Taking it to the store was out of question, because of time constraints. Only thing I had handy is the above mentioned tool.
Here is for creativity: I only had a trickle charger with me + a John Deere gator. Obviously the trickle charger was not designed to start up the big diesel engine, and the battery in the gator was way below the necessary cca.
The small battery wax enough to preheat the plugs, and the trickle charger combined with the running gator was just enough to turn the engine over. And now here is where I am waiting for better ideas…

The directions in my old battery charger explains how to check the condition of the battery cells, and state of charge by the specific gravity of the electrolytes using a hydrometer. So maybe you can get a battery hydrometer at the auto parts store to test the battery. Keep in mind that batteries can be dangerous with acid a possible explosion so follow all safety directions that come with it. This obviously cant be done on a none serviceable battery.

There are a lot of youtube videos on how to check batteries so go on youtube and enjoy.

@252525 … Harbor Freight sells an inexpensive gadget to test a car battery under about 100 amps of load.

http://www.harborfreight.com/100-amp-6-volt-12-volt-battery-load-tester-90636.html

I would deal with this the same way I dealt with a dying house battery on a motorhome (a large lead-acid truck battery). I removed the battery, put it in the trunk of my car, and hauled it down to the auto parts store to get it tested. Then I came home with a new battery (and some new straps since I had to cut the straps to get the old battery out) and installed the new battery. The whole project took less than an hour.

There are time constraints and there are time constraints. I can see why you would prefer to diagnose this without removing the battery, but if you had removed the battery and had it tested, you’d likely be done now with a new battery installed or the battery ruled out as the cause. Sometimes seeking a shortcut can make something take twice as long.