Hard to start after sitting a while

I've recently just bought a ZR TD, everythings fine apart from on mornings when I try starting it takes about 5 seconds of turning over to start. but if you switch the engine off and try start it again it starts fine.



I was thinking either glow plugs or battery, my battery does seem on its last legs (it goes flat if not used for 2-3 days)



Another thing is it has had a new fuel pump put on so would that cause this problem?

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