Car battery advise multi metering and readings

[silverdale]

My car seems to struggle starting at the moment. I've only had the car a few months so I checked the battery with a multimeter. It's showing 14.2 when running and 12.3ish when cold but when I start it it's only showing 8-8.5. Is this a knackered battery ?.
I did some reading and there's conflicting things going about. Is it right the CCA (cold cranking amps) has to be above 10 or its basically knackered ?

 

[bluepassat]

Check the battery voltage in the morning when left overnight should be 11.50 volts or more before you try and crank

If your alternator is not charging enough...it should show over 14.00 volts idle no loads, at the battery terminals

And with all your loads on lights heated windows etc 13.70 volts minimum at 2000rpm this show a good alternator if all ok then get your battery tested

 

[sneaker]

If it's getting as low as 8.5 volt, I would change it.You could try charging it with a proper battery charger, but if you are getting 14 plus volts when the car is running it sounds like the regulator is working ok, and it is not holding charge.

 

[ketmp]

I've never tested a battery whilst at same time trying to start the engine so not certain what voltage should be at that specific point.

As mentioned earlier, once car started and no electrical demand you should get 14v plus which you are so that points to charger appears fine.

For an accurate reading of battery you need to leave overnight and check first thing in morning without starting engine or with no other electrical thing on in car.

However, reading should be around 12.2v for a partially discharged battery. 12.5v+ for a fully charged battery.

If it's 12v or less I would say battery is totally discharged.

 

[miggy]

How old is your car?. If it's 3 to 5 years old with the original battery it is probably knackered. It sounds like your alternator is working so if it's not your battery you may have a lazy starter motor (tight) draining your battery as you try to start the car.

 

[silverdale]

Turned out to be a knackered battery. I tested it again and the CCA dropped to below 8. There's a eurocarparts not far from me but it's far cheaper to use click & collect and a 10% code + quidco gets you 20% off.

I've just put it in and ran it for 1/2 hr round the block and it seems fine. Before the clock would reset every time I started it up but now its seems to be holding charge and the clocks not resetting. The other thing I was getting was random error lights i.e Diagnostics and air bag light on start up , they've stopped so hopefully it was just the battery and not a new alternator or starter motor , , thanks to all for for the advise

 

[thebigman]

a charged battery should be able to maintain above 10 volts for min of ten seconds while cranking. If it can't it'll have a bad cell.

 

[D 8 RCS]

Just as a point for anyone else who reads this, does your car have "Stop, Start" technology ?
If so that is the cause of the problem, numerous owners of a lot of different makes of cars with "Stop, Start" technology have reported the same problem. The Stop, Starting causes the battery to be drained at a ridiculous rate particularly driving in town.
Most models do have the option to turn the "Stop, Start" off, which is what I would advise, because the mpg increase is minimal and when the cost of new batteries is taken into account it is more expensive to run.
The only good thing about "Stop, Start" is the imaginative mpg figures it gives for the manufacturers.