Why is my Jaguar X-Type failing to start?

I have a 2007 Jaguar X-Type 2.0 diesel manual. It only has 38,000 miles and drives fine with no funny noises or handling issues. Lately it has shown an odd starting problem. When it's cold after standing for a few days the engine cranks really slowly as if the battery is dying but when I turn it off and try again it starts fine. I've put a new battery in and had the earth leads replaced due to corrosion, but they haven't solved the slow cranking problem. Auto electricians have tested everything but found no obvious faults. Any ideas?
Did the auto electricians actually test the starter motor and the relay? It would appear to be a intermittent contact/electrical problem. Does it turn over slowly each time you leave it for a few days? If so, you could have an electrical fault that is discharging the battery. Next time you leave it for a number of days check the voltage of the battery before trying to start it. You should get around 13.5 volts across the terminals. If you have 13.5 volts then you could try a direct connection to the starter, thereby eliminating the circuitry. However, if it still turns over slowly then suspect the starter itself.
Answered by Alan Ross on

Ask Honest John