Cold start

Good guys I'm having a problem since i got my disco 300tdi .
in the morning she wont start so i jump it with my wives car then she runs but takes a wile to do so Aswell
so I changed the 657 battery to a 650 battery the cca 880 its turns better but still no start i went and change all the earth cables .
checked the clow plugs Aswell.

But when she starts and runs for a bit u switch of she starts one time is there anything im missing .

Possible air leak in the fuel lines if it turns over well but not starting. Make sure you have fuel at the lift pump, injection pump and injectors.
Make sure you have no leaks on any fuel pipes including leak off pipes. Check connector on fuel cut off solenoid. Might also be worth changing fuel filter.
Advice is general as never had a 300tdi but son has 200tdi so presume it's similar.

As above, should start instantly even without glow plugs, so fuel will be the problem