Is My Battery Being Charged Correctly?

[Alickadoo]

My wife's car - strictly speaking. It's a petrol Yaris, automatic, 2002 - yes, I know, 80,000 miles and I am concerned that the battery is not being charged correctly.

I have a little plug in volt meter in the cigarette lighter socket and it shows around 12.3 volts when the engine is not running. Is that correct? The car is coming up to its annual service - should I ask the garage to check the charging? Voltage regulator - is that the word?

The car had a new battery in January and I am not convinced that it is fully charged.

Forgive my ignorance - what do I ask for?

[Panamax]

100% fine.
Unplug your voltmeter and get on with your life.

[ARHarh]

First the cars charging system is likely to be far more accurate than a cheap plugin meter. The car will tell you if its not charging properly, they have been doing this since the 1920's.

As suggested unplug the meter launch it into the bin and find something more interesting to worry about

[SlimJim16v]

They're not very accurate. It's what it says with the engine running that matters.

[Scrump]

What does the voltmeter say with the engine running?

[E-bmw]

A fully charged battery in good health at rest should be around 12.6v.

A battery under charge with the engine running is more likely to be around 14.2v.

As others have said, accuracy is the key, so how much higher does it go when running?

If it only goes to around 13.5v then the meter is reading close to 0.5v low in both cases & it is likely that, that is correct for that meter in that car.

ETA.
If you think you have the symptoms of a problem, let us know, otherwise just get on with your life.

What type of journeys does it normally have?

Lots of short/a good mix/long journeys only etc.

Edited by E-bmw on Sunday 23 March 18:33

[Chris32345]

Alickadoo said:

My wife's car - strictly speaking. It's a petrol Yaris, automatic, 2002 - yes, I know, 80,000 miles and I am concerned that the battery is not being charged correctly.

I have a little plug in volt meter in the cigarette lighter socket and it shows around 12.3 volts when the engine is not running. Is that correct? The car is coming up to its annual service - should I ask the garage to check the charging? Voltage regulator - is that the word?

The car had a new battery in January and I am not convinced that it is fully charged.

Forgive my ignorance - what do I ask for?

12.3 is Quite normal by the time it gets around 12v port

[Simon_GH]

Plus if you’ve turned the ignition on to make the 12v socket live then you’ll be running a fair few electronics even on a 23 year old car.

[Alickadoo]

Scrump said:

What does the voltmeter say with the engine running?

Not sure, I will look in the morning and report back.

[paul_c123]

Unless you can measure current, you can only guess that the battery is being properly charged. You can buy a DC clamp ammeter, however on about half of modern cars the battery cables are so tight or there's multiple connections, you can't get around them (or all of them) properly to measure it. Don't try and use the ammeter on a multimeter, you will fry it when you try start the car. Even loads associated with switching on modules etc on unlocking go about 10A so its dodgy even for that.

[E-bmw]

paul_c123 said:

You can buy a DC clamp ammeter,

Can you link/tell me of a manufacturer that does such a thing in any more than mA as I can't find one & have been looking before?

ETA.
One for a reasonable price that is, as £150 for something that will be used 5 x isn't a good investment in my eyes.

Edited by E-bmw on Monday 24th March 08:09

[GreenV8S]

paul_c123 said:

Unless you can measure current, you can only guess that the battery is being properly charged.

That's all true, but if the charging system is pushing the battery voltage up to around 14v then you can be pretty confident that it's doing its part - if the battery doesn't take charge with 14v applied to it then that's a problem with the battery, not the charging system.

[Simon_GH]

If a battery was fitted in Jan and its now 2 cold months later, I’d be pretty happy the charging circuit was working.

[Alickadoo]

E-bmw said:

A fully charged battery in good health at rest should be around 12.6v.

A battery under charge with the engine running is more likely to be around 14.2v.

As others have said, accuracy is the key, so how much higher does it go when running?

If it only goes to around 13.5v then the meter is reading close to 0.5v low in both cases & it is likely that, that is correct for that meter in that car.

ETA.
If you think you have the symptoms of a problem, let us know, otherwise just get on with your life.

What type of journeys does it normally have?

Lots of short/a good mix/long journeys only etc.

Edited by E-bmw on Sunday 23 March 18:33

Thank you for your reply.
Update.
After standing over night.
Ignition on, before starting 12.0
Engine running 13.9 - 14.0, settles to 13.8-13.9
The display switches to 0.3A, or 0.4A, I think it reads.
Engine warm, but not running, immediately after switching off 12.9 or 13.0.

What should I make of all that?

[E-bmw]

Alickadoo said:

E-bmw said:

A fully charged battery in good health at rest should be around 12.6v.

A battery under charge with the engine running is more likely to be around 14.2v.

As others have said, accuracy is the key, so how much higher does it go when running?

If it only goes to around 13.5v then the meter is reading close to 0.5v low in both cases & it is likely that, that is correct for that meter in that car.

ETA.
If you think you have the symptoms of a problem, let us know, otherwise just get on with your life.

What type of journeys does it normally have?

Lots of short/a good mix/long journeys only etc.

Edited by E-bmw on Sunday 23 March 18:33

Thank you for your reply.
Update.
After standing over night.
Ignition on, before starting 12.0
Engine running 13.9 - 14.0, settles to 13.8-13.9
The display switches to 0.3A, or 0.4A, I think it reads.
Engine warm, but not running, immediately after switching off 12.9 or 13.0.

What should I make of all that?

Assuming all of these readings are on the same meter it is at least reasonably accurate (going by the time of the 14.0 & 12.9/13v readings) which would be telling me that the battery is weak as when initially turning it on I would like to see over 12.5v.

Having said that a small petrol-engined car is the easiest environment for a battery to be in, especially approaching warmer months.

Perhaps take it on board that it will likely need changing before next winter & get one when they may be cheaper/less of a stress-purchase.

All of this is assuming that it had been for a good drive/charge up before it was put to bed yesterday, if it didn't then do that first & check again.

[ARHarh]

Does the car struggle to start? If not don't worry, you will only be able to diagnose battery issues with a decent calibrated meter on the battery terminals. Or a proper battery tester. Do not rely on a socket which could have dirty contacts and an uncalibrated meter. After all you are talking less than 2% below what to expect at the battery terminals.

But with those numbers I would have no worry's at all.

[Alickadoo]

The battery was new in Jan/Feb of this year.
What do the 0.3A/0.4A displays mean?

Any road, it's having a service and MOT this week. I have asked them to check the charging rate etc.

Thanks for all the replies.

[paintman]

If the car is only being used for short journeys then it may be that the alternator isn't bringing the battery up to a full charge, esp if you're also running blowers, heated window, headlights etc.
This would be entirely normal, alternators are intended to run the vehicle electrics once the engine is started & to keep a fully charged battery topped up, not recharge a battery.
https://www.optimabatteries.com/experience/blog/fa...
(Ignore the 'red top 'blue top' blurb at the bottom)

Get yourself a mains battery charger & fully charge the battery before doing any more messing about with 'little plug in volt meters'.
You can then check the voltage after leaving the battery off charge ovenight.

A very rough guide to state of charge - note the comments about possible causes by the big red X in the notes:
https://www.thebatteryshop.co.uk/car-battery-volta...

I wouldn't be in the least surprised if some garages didn't see a golden opportunity to pull your trousers down & sell you a new battery & alternator.

Edited by paintman on Monday 24th March 12:57

[paul_c123]

GreenV8S said:

That's all true, but if the charging system is pushing the battery voltage up to around 14v then you can be pretty confident that it's doing its part - if the battery doesn't take charge with 14v applied to it then that's a problem with the battery, not the charging system.

There's a small possibility it still shows (say) 14V but isn't sending much current into the battery, that's why the "gold standard" is to actually measure the current. But yes, you can infer more/less what you need from voltage readings. I mention it because its the gold standard. And its useful for other electrical troubleshooting scenarios.

I bought mine about 2 years ago for £27.59, make sure if you buy one it can do DC amps as well as AC.

[Alickadoo]

paul_c123 said:

There's a small possibility it still shows (say) 14V but isn't sending much current into the battery, that's why the "gold standard" is to actually measure the current. But yes, you can infer more/less what you need from voltage readings. I mention it because its the gold standard. And its useful for other electrical troubleshooting scenarios.

I bought mine about 2 years ago for £27.59, make sure if you buy one it can do DC amps as well as AC.

Thank you for the advice, but I don't think I am going to be buying any more bits of kit which I don't understand.