Car Battery Check

[Nijinski001]

Can I check a car battery with a multimeter and if so what am I looking for to assess it's effectiveness?

 

[Hallsy]

You can test a few things that may highlight obvious problems but it is diffuclt with just a meter as it has no load when connected to battery.
Anyway, with ignition off and meter on V d.c. you should see around 12V across the battery terminals.
Now turn ignition on, turn on fans, lights, demisters, radio, etc and see that the voltage across the terminals doesn't drop below 12V, with the alternator doing it's job properly you can expect to see anything up to about 14V.
If all that looks OK but you are still having prolems with a battery going flat check for any current draw when the ignition is switched off, do this by putting your meter on A dc , disconnect the battery earth and go between earth cable and negative terminal on battery. You may have a small current draw due to car stereo memory, etc but anything significant would indicate that you have a circuit dragging down the battery somewhere, i.e. a fault.
HTH.

 

[ban-all-sheds]

Why do you want to test it?

What feature do you want to test? The ability to hold a charge, or the ability to deliver high current?

Are you having problems that you think might be battery related? What are the symptoms?

How old is the battery?

 

[JonB]

Kwik Fit are doing a free digital battery check at the moment, (whatever that is)

 

[ban-all-sheds]

It's probably the same idea that has been used for donkey's years - stick a large load across the terminals (several hundred watts) for a bit, and see how well the voltage holds up.

Only with a digital meter instead of analogue.

There isn't much else you can do to test a battery, as that's all it has to do - store charge, and deliver it at a high rate when asked.

<Edited for spellnig misteak>

 

[Hallsy]

Well, for started you can do as I suggested, if you get any siginficant volt drop just with a few things on like heaters and lights then the battery isn;t all that, measuring the voltage whilst cranking will give a good indication as well, after all this is the biggest load that the battery is likely to take.

Oh and BAS, technically a load isn't measured in watts, watts is a measure of work done or power output

 

[ban-all-sheds]

True - it was sloppy. Should have said something like "which would consume several hundred watts from a healthy battery", or "which would draw several tens of amps from a healthy battery".

 

[Hallsy]

Haha, was only pulling your leg

 

[ban-all-sheds]

No - I think you were right. The load has fixed characteristics, but the amount of work that it does is not fixed.

 

[Spark123]

Ever used a hydrometer?

 

[Nijinski001]

Now turn ignition on, turn on fans, lights, demisters, radio, etc and see that the voltage across the terminals doesn't drop below 12V, with the alternator doing it's job properly you can expect to see anything up to about 14V.

I presume you mean inginition on and engine turning?

Spark123 - A hydrometer isn't much use with a sealed battery is it?

 

[Spark123]

Are there no covers you can take off to get access?

 

[Nijinski001]

Sorry Spark it's looks completely sealed

 

[Spark123]

They don't make them like they used to.....

 

[Hallsy]

Now turn ignition on, turn on fans, lights, demisters, radio, etc and see that the voltage across the terminals doesn't drop below 12V, with the alternator doing it's job properly you can expect to see anything up to about 14V.

I presume you mean inginition on and engine turning?

Spark123 - A hydrometer isn't much use with a sealed battery is it?

Yep, I'd see what sort of volt drop you get when cranking the engine, so get someone to start it whilst you check, then once it's running check voltage with all accessories on, with gentle revving of engine and alternator doing it;s job you should see around 13-14V really.