200 tdi battery

hi all
the battery fitted on the car has a cca of 540 anyone know if this is the correct one as fine in summer but soon as drop in weather it dies after 4 turns of the engine.battery is 18 months old .when i bought it shop said it was correct one but some how i feel it under powered ive had alternator tested and this is fine, also if car left standing for 3-4 days even the alarm light dies on dash and central locking stops. cheers in advance.

510 cca std - 550 hi power

I've got 2 Tractor batteries - 860CCA 120Ah on my 200TDi fender.
I never have a battery problem.

if your battery is dying after a few days it must either be knackered or you have a drain somewhere! check the earthing points or try cleaning the battery terminals.