Can a car battery measuring 12.4v still be knackered?

Car failed to start this morning. Jump started very easily. Wouldn’t start again tonight but again jump started very easily.

Got home and got the volt meter out. 14.1v with engine running. 12.44 without.

All seems normal to me.

After a run it started fine straight after turning it off. But at the second try after failed again.

When it fails there’s no aren’t to turn over, just a clicking, the dash dials moving and the CD changer shuffling.

Is the battery knackered but still giving a good reading? No problems prior to this morning and didn’t leave lights on or anything.

I’m no expert, but in the true spirit of this forum, I’ll speak as if I am…..
Presumably, 14.1v is the output voltage of the alternator – a good sign, sounds like it’s charging ok.
12.44v sounds a little on the low side – I reckon you’re due a new battery!

Yeap, its not holding enough amps.

Sounds like it to me.

That does not sound like a knackered battery to me.

I used to jump start my car every 3 days when my battery was knackered.

At one point I only drove my car 2 or 3 times a year and the battery got drained but once I jump start it, the car would start no problem and I could drive normally. But once I left it again for a week without starting I would have to jump start it again.

Put it this way once I jump start it on the day the car would start easily no problem for the entire day or the next day, so long as I drive it around.

Ya, get a new battery … I swapped my battery around with engine running and jump start cable attached because I could not find the bloody radio programme code … dammit. Don’t do it my way …

Now with new battery everything is running fine but I am still not driving often … hmmm

Actually, I’ve had this.

Spent about six months with it sometimes starting perfectly, sometimes going “click.” Went through a rake of mechanics and auto-electricians to no avail.

In the end I took it directly to Lucas, the princes of darkness themselves, who diagnosed a faulty rectifier on the alternator inside of 30 seconds. Swapped that and it was fine ever after.

Turn engine off, headlamps on for 5 mins. This removes any surface charge. Maybe even try n start it. Lights off. Check voltage while cranking, below 9.5 volts. Battery is stuffed

Cougar – Moderator

In the end I took it directly to Lucas, the princes of darkness themselves, who diagnosed a faulty rectifier on the alternator inside of 30 seconds.

Mine is just normal knackered battery because I did not drive often (was on provisional license then).

Now I drive once or twice a week.

If you drive often or every day and you have to jump start then it might be as Cougar suggests …

It’s knackered.
Volts mean very little when checking batteries, it’s the Amps that are important.
Get yourself down to a trade supplier (Gfs, eurocarparts etc), it’s easy enough to fit yourself.

Halfords used to do a free battery test. Could be worth a try, as a straight up voltage test with a multimeter isn’t an accurate indicator of a healthy battery.

Turning over slowly, and getting slower…usually an indicator of a dying battery in my experience. Not turning over at all could still be a dying battery, but could also be all manner of things. A sticking starter motor, faulty immobiliser, etc. Could be a poor ground somewhere. Something like that.

I’m no expert….just been through it all before! Basically a process of ruling out battery. Checking that power is getting to starter. Starter is operating correctly. Etc. Jump start would indicate battery anyway, so it’s unlikely to be anything else.

Or after doing all that swap a 6 quid ignition switch over and bingo.
Although the starter motor was on the way out so that got swapped over.

A good battery will normally hold about 12.8 volts when fully charged. More if let the engine has just been running and charging the battery.

12.7 is a charged battery.

12.4 is knackered.

Most motor factors and Tyre companies will do a free battery check.

As Trail Rat said – 12.7 is charged, 12.4 is dying.

As above. 12.8 is normal. 13.8 is typically fully charged (on charge). It’s knackered

Metered a battery can be 12 v and yet under load drops off significantly. The testers use a device with a resister in to make the battery work to measure the amps under load.

As the guys above say, the proper battery test tool uses a BFO resistor to load the battery up and measure what amperage it can chuck out. But it’s a pretty specific tool so it’s only really of use if you sell a lot of batteries.

The home mechanic method is to charge the battery one day, disconnect the charger and leave it overnight, if it’s not got 12.8V in it the next morning, it’s on it’s way out.

Cheers guys. Battery ordered.

It would probably die on the first cold morning of autumn anyway. Best done now.

PS seeing the mechanic with a 30-Amp discharger is impressive.

Voltage alone is a pretty poor indicator of battery condition.
And I’ve seen plenty knackered batteries that can still pass a test using a drop tester (the proper name for the old fashioned tester mentioned above).

Charging voltage on something without stop/start should be above 14V with all loads on. Modern stop/start systems with smart alternators can vary the voltage quite a bit with anything between 13-15V being acceptable depending on numerous sensors/conditions, so you’re basically at the mercy of the alternator or ECU telling you there’s a charging issue.
You’ve also got to be aware of AGM batteries (fitted as standard on stop/start vehicles, but often fitted on non stop/start depending on the application), as if they’re discharged, the charging voltage won’t rise until the battery is reaching fully charged (this is mainly why AGM is used, as they’ll absorb charge far faster than a conventional lead acid battery).

Cranking voltage on a normal car I wouldn’t expect to drop below 10V with a well charged battery, but if it’s nearing discharged, below 9V and still cranking is borderline acceptable.

Modern battery testers are all capacitive discharge, which give a far better reading of battery condition. In a nutshell they apply a low current frequency through the battery, and with some clever electronics tell you what kind of condition the battery is in. They’re not entirely fool proof, as I’ve once seen one pass a battery as ok, yet still see the battery voltage plummet on load.