Is my Battery Knackered?

[Henry_b]

Hello Gents/Ladies

I have a 2005 Jaguar S type and I'm having a spurious fault with "cruise not available" popping up on the dash..

Forums said to check the battery, and after 2 days sitting it drops to around 11.9v it still starts but not very enthusiastically


Reading online everyone says anything below 12.2v is a knackered battery..

The batt fitted is a Lion unit, which it seems isn't the best of brands, also coupled with the fact it has been run down a few times does this point towards a knackered battery?


Thanks

H

[SS2.]

Assuming your meter is accurate, 11.9v after just a couple of days of sitting idle is pretty poor.

What voltage do you get when the engine is running ?

[Henry_b]

The voltage when running is 14.5 so the Alt is working well..



Cheers

[SS2.]

Assuming the engine has been running long enough to the replace the charge lost through starting, then it does sound like the battery could be on its way out.

[anonymous-user]

Henry_b said:

Reading online everyone says anything below 12.2v is a knackered battery.

Correct. Buy a new one.

Good battery should show at least 12.6v
Decent battery should show at least 12.4v
Anything 12.2v or less is knackered.

N.B. Voltage measured after being left to stand overnight at this time of year (not mid-winter) and measured with a decent voltmeter.

At the end of the day the only way to truly test a battery is with a high current discharge test at your local battery specialist. But leaving that aside, if a battery's over 2 years old and you're having any problems at all just buy a new one.

Spend your money on batteries, not on chargers.

[Henry_b]

Okay yep I think you're right, i took her on a 70mi drive and it was down to 11.9 in 2 days, so battery is goosed I think.

[Spare tyre]

Brake lights working?

Tow bar fitted?