Testing for Knackered battery or a drain

Car battery keeps going flat. Battery was new in September.

Charged it up.
Few days later measured 12.89 or close.
Didn't use the car for another few days and it read 12.19.

If I disconnect the battery from the car and measure voltage over a few days, will that show me if the battery is knackered and losing charge?

If it doesn't lose charge when disconnected, I can assume its drain from the car?
If so how the heck do I find the drain?

I have a basic multimeter, but little idea how to wield it!

Any help appreciated

 

You need to identify what circuit the current is leaking from,
So turn everything off, multimeter set to measure amps, then bridge each fuse in turn with the meter to find what circuit is drawing current, once identified, then start chasing individual components on that circuit, disconnecting them/isolating them until you’ve got no current drain.

 

Lovely, thanks very much.

I just found this video that says the same and exactly how to do the testing.

Cheers

 

Modern car may draw 1/4 amp or more keeping all that electronic junk on standby. Nothing wrong, just rubbish by design.

 

Have I set the multi meter up correctly?

Or perhaps I haven't actually got a proper drain.

First picture is set to 10a (20m) and settles at a reading of 0.11 after a few seconds.


Second picture is when it's set to 2m and reading after settling is: .011


If I had a proper drain shouldn't it be a few amps?
I did a reading with internal light on and it read 3amps.

This test was just from removing the negative battery cable. Red probe on negative battery cable clamp. Black probe on negative battery terminal, like it showed me in the video.


If these readings are right perhaps my battery is just knackered?

 

Cheers Mike.

I know there should be a small draw from my stereo etc but that shouldn't be enough to flatten by battery in less than a week.

Will you look at my figures /testing above in case I've made an obvious error please

 

Perhaps it's first worth disconnecting the battery from the vehicle. Then place the ammeter between the disconnected cable and the battery terminal - what is the reading? If more than 250mA then the fault is likely a drain through the vehicle components. Check as advised above.

Then charge the disconnected battery with an external trickle charger. Disconnect and write down the voltage readings over the next few days. If you again see 12.19v after a few days as in your original post, it looks like the battery is useless.

 

I thought that was what i had done above wasn't it?

 

think its all been said above. might also want to check charging voltage (if it will start).c 14 volts

 

yes

 

Checked charging voltage the other day and that was fine at 14V +

It's the amps/drain side i don't really understand, but if i've set it up correctly and the readings are right then it points to a dodgy battery

 

yep!

 

Just because it is new doesn't mean it is OK. I bought a Halfords battery last August - had to take it back last week - they tested it with their gismo and they confirmed it was knackered - so got a new one under warrantee.

 

Have I got this right, Paul?

On 20 milliAmp scale??? it read 0.11, does that read to you as 110microAmps?

 

If the test meter plugs were still in the 10 amp sockets, then the "current" reading will still really be 0.11A , just the decimal point position got moved as the range switch was rotated.

0.11Amps is the sort of drain that a car stereo with Bluetooth might have, listening all the time for devices to connect to it. . So the battery will go flat in e.g 65 AH /0.11A or 585 hours or 3 weeks 3 1/2 days.
Probably not a bad battery , or it was not until you let it go flat a few times.

Like on my bus with my Sony MEX3900BT where I have to pull the fascia panel when I stop using it or it drains 0.26 amps. Without the fascia, the drain is not really measurable.

I do have a tester tool, which I always have with me in my bus that does a simple test to determine the percentage CCA rating of a battery .. so it does percentage knacker factor.
They cost about £24 on eBay, but I found a broken older one for a fiver at a boat jumble.

https://www.ebay.co.uk/itm/-/384791698086

 

Ok that 110mA makes more sense


I am used to an autoranging meter, makes you lazy, I guess.

 

But even then , usually for the high current range you have to move the probes over to the 10A or 20A socket, as the other 2000mA/volts/ohms socket has a 2 amp fuse.. .

 

im a lazy fluke user what are these other sockets he mentions?

 

I have no idea, I am a lazy Fluke user too!

Paul's meter scales just seemed odd to me ! 110mA, I can live with that, but why get smaller when the scale goes down

 

I think its 11mA