correct battery voltage

I know I'm pushing things here (I will be if I don't get this sorted)
My son has a Rover 100 1.1 (I know its not a land rover but please dont discriminate or refer to this car as a 'metro' it has feelings)
Battery has been playing up. Seems to discharge over a few days. If I jump start it and run it for 20 minutes even though the alternator is kicking out 14V if I leave it half an hour it will be flat and will not start the car.
Its just over a year old its a unipart 063. I charged it overnight but as soon as I remove the charger leads the battery voltage drops rapidly from 13.2V to less than 12.8 then over the next day down to 12.5V

What should the voltage be on a healthy fully charged battery?

I took it back to unipart who have had it on charge and given me this explanation:

"The battery is worn out, it does not have any manufacturing defect therefore is not under warranty"

Not impressed.

Its not the volts you need to worry about its the Amps.
and it sounds like you bat is a ex bat.

Voltage drop is an indication of an internal cell failure. I just wondered if anyone knew what the correct voltage should be thats all.

normal is 12.6v

anything below 12.4 requires a charge. if its not holding a charge, then the battery is duff.
and that feckin unipart warranty is shyte.

They are going to charge it overnight and see what its like tomorrow, thinking about it the car had been standing about 2 months when we noticed it was flat. Saying that, my boat has not been used since last sept. Tried it the other day and it started straight away (evinrude 70) I'm not convinced its OK

2.2v per cell, 6 cells =13.2volts

most companies will just change a duff battery if its less than 2years old, if they dunt then shout at head office

Leaving lead acid batteries for a long time with no charging does knacker them. If you're going to be leaving a car unused for a long time, it's probably worth removing the battery and putting it on a "maintenance charger", like an Optimate.

You can get batteries that are more resiliant to abuse, Odyssey are a make I've have good results with, Expensive though.

he says that the battery falls to 12.5v after 24 hrs, with no useage!
not after a few months!
that clearly shows the battery is more than likely feckin duff.

and it fails to start the car after 20 minutes!

Skip it and get a new one... £20 for a bosch for that size car battery in Costco.

well said mate.
i kwow some of us runs our cars on tight budgets, but 20 quid ffs!

ive seen torches dearer than that!

Its not the £20 its the principle of people standing by their warranty promises!

Well I'm pleased to say that sticking to my guns and not compromising on the Unipart warranty issue has paid off. Today I received an new battery with a 3 year warranty.

well done mate.
and good on unipart too. although they should have done it wifout u shouting from the rooftops.