Quoting TomWoodis: Ok, so last night I put the car on the charger so it was fully charged this morning. At standstill with the engine off, the voltage was showing 13V. Pretty good but I guess expected given it was fully charged. I then started the car and at idle, the voltage was 14v which I thought was pretty good. Leaving the car a while to warm up so that the fan finally came on saw that figure drop to 12.8v. With the headlights also turned on, the voltage was showing a bit less and appeared to be dropping the longer I sat there with the voltmeter. The biggest change in voltage appeared to be when the fan came on.And if you lift it to 3,000 rpm when it's dropped to 12.8V what happens?
Jonathan