when you turn the key and the electrics come on, have a look where your battery needle is pointing on your dial, and when you start the car does the needle go anywhere, i've just bought a battery (but not changed it yet) 3 days ago as when I put my key in the needle is pointing to below 9v, and the car struggles to start, but when running the needle goes up to 13ish, which is the right place, suggesting that the alternator is doin its job still, i'm gonna stick the new battery in 2moro cos if I leave the car unused for 24 hours it just won't start, but i've been lazy about it
new battery from the dealer is £71 inc vat at the moment