Hello all,

I've got a 2003 WRX with a 390 AMP, 12V battery and I wonder if anyone can tell me if the below is correct.

I've been told that the voltage for a "cold start battery" (i.e. testing it before you start the car) should be roughly 12.7V for a battery at the start of it's life and 12.2V when it's virtually dead.

When switching the engine on the alternator should raise this to roughly 13.5V.

Mine currently reads 12.4V for a "cold start" and with the engine switched on the voltage does rise to roughly 13.5.

Does this mean that my alternator is working correctly but the battery could be on it's way out

 

if the batteryvoltage is 13v+ with the engine running, then it sounds like the alternator is charging (13.5-13.8 is normal

the battery voltage without engine running is dependent upon charge and whats running (without the engine running) ...like alarm etc.
less than 12v suggests you arent charging the battery enough (too many short trip siwth lights on, ICE running etc.?) above 12v is prolly fine

 

given the age of the vehicle providing that the battery is oringal one from the factory that the battery is at fault

thanks matthew

 

Cheers all, I've replaced the battery now and all appears fine