12v lead acid car batt

[PabloPicasso]

I came home after a week away and my car wouldn't start. 20 min with an old mains charger and she turned over and started fine. Drove around locally to shops etc. All started fine.

Batt showing 12.3v 30mins after parking. Couple of hours later its only showing 12.1v, all on my circuit tester.

Is that a dud battery? Apologies for the non boaty nature of this question.

 

[Fr J Hackett]

Give it a decent run to charge then if it does the same yes, new battery required or risk flat battery if you leave it for any length of time.

 

[Biggles Wader]

Or something is draining the battery. Does that light in the glovebox go out? Are you sure?

 

[billskip]

What is the voltage at 2000 rpm?(in neutral of course)

 

[andsarkit]

Possibly on the way out but you won't know for sure unless you fully charge it.
Assuming a 70Ah battery it will take about 20 hours with a 5A charger.
Then check voltages again after it has rested for a couple of hours.

As said above, also check for unwanted loads (interior lights etc) and that the alternator is giving out 14.4V.

 

[PabloPicasso]

What is the voltage at 2000 rpm?(in neutral of course)

14.1v. Reving the engine didn't seem to alter it at all.

 

[billskip]

14.1v. Reving the engine didn't seem to alter it at all.

Ok ,so assuming you dont have any devices, security or gps which will possible use up to 500ma when ignition shut down its possible the battery ..

 

[PabloPicasso]

Yes. Seems likely

 

[rotrax]

Unless there is a current draw when not in use it sounds like the battery is Donald Ducked*.


* Cockney ryming slang. Should be easy to work it out

 

[Martin_J]

Whereabouts are you? I've got a battery tester in the boot that can test health in half a minute...

I know they cost as much as a new battery but they really save time and let you know instantly)

They can show a 100% state of charge but poor state of health..



And also the available CCA.

 

[Martin_J]

Not necessarily the same battery but it'll also show load and no load charging



And this wasn't my car but you even get cranking time shown..

 

[PabloPicasso]

Whereabouts are you? I've got a battery tester in the boot that can test health in half a minute...

I know they cost as much as a new battery but they really save time and let you know instantly)

They can show a 100% state of charge but poor state of health..

View attachment 164723

And also the available CCA.

View attachment 164724

Very Generous of you buy no good for me if you're in the UK

 

[PabloPicasso]

Just checked it again and its 11.98v. Motor wouldn't turn over on the key

I'll get a new battery.

 

[Martin_J]

Very Generous of you buy no good for me if you're in the UK

I guess it would need very long leads to reach..

 

[wingcommander]

14.1v. Reving the engine didn't seem to alter it at all.

Alternator is ok then .

 

[Momac]

It pays to get a new battery before the dud battery damages the alternator.
And before the dud battery fails completely .

 

[MontyMariner]

Just checked it again and its 11.98v. Motor wouldn't turn over on the key

I'll get a new battery.

Good time to replace it as we're fast heading into winter!

 

[B27]

It's 'probably' the battery, but with a modern car, it's not 100% sure on the info given.
Modern cars do not have alternators pumping out a steady 14 point something volts, they have clever alternators which faff with the voltage to optimise mpg, battery life etc. My current car is over 12 years old and has this. Stop-start cars will have this.

To be sure, you really need to properly charge battery overnight, or use a tester or interrogate the car's OBD.
A short charge and a short drive is not enough to be sure.

OTOH, if the battery is quite old, getting a new one is not a bad thing.
8 years is a typical life these days.

 

[billskip]

Well the model make and year hasn't been mentioned....model T ?

 

[PabloPicasso]

Not far off. Its an 06 automatic Ford Focus. No stop start nonsense. Its been pretty good overall and I've had it since 2008. Nothing flash about it but it does everything I want it to, accept start!!