Starting Problem??

I have an odd problem with my TDi 300 Disco. It has always been slow when turning over on the starter but it starts so well that has not been much of an issue, unless the temperature really drops. When it is very cold, I have to use my Power pack to start it. Once started it then starts all day long....until the next morning.
I checked my alternator and it is putting out about 14 volts so no problems there.
I changed the glow plugs, no change.
I bought a new battery, no change.
I recently had a rocker shaft snap and ended up having a complete engine rebuild. When re-fitted, the earth leads were cleaned, still no change.
I was told that there is something in the back of the starter that can burn out? I replaced the starter with another that was working perfectly on the Disco it came off as I had tried it out. No change.
Does anybody have any ideas? It just turns over slowly, not quickly like the other Discos and Land Rovers I have heard. With the Power Pack on it starts instantly. It seems as though I am losing some current somewhere but I have run out of ideas!!
Cheers
Steve

sounds as though you have something draining the battery over night.
with all the power off and the vehicle standing check to see if you have a drain of power....
also check the obvious, i know its daft but i had a similar problem which turned out to be one of my kids turning the rear interior light on...
the passive alarm only uses minimal power... also check the radio isnt draining the battery due to a fault..
hope this helps

Thanks for getting back to me.

I suspected the battery early on. I replaced it about 9 months ago. If I check the battery voltage it shows full and it drops to about 8.5 ( I think, I need to check) on cranking. It doesn't appear to be draining overnight. It is only in the winter with extra cold mornings that I have the problem. If I charge the battery fully, the starter doesn't noticeably turn over any quicker.

Hi if your battery drops to 8.5 volts on crancking it is to low should not really drop below 10v,have you tried putting another earth wire on it or just using a jump lead on a good earth to check it does not need another earth strap i have read you have done this but best to check as the 300 ends up burning out the handbrake cable if bad earth,alternators can cause a drain overnight and backfeed loosing current,failing any of these being wrong get your battery rechecked as it could have a doddgy cell,my car is a bit sluggish now first year i have had this problem so i charge mine up every couple of days as i dont do many miles during the week only about 50 with lights on morning and night and it starts fine,hope some of this helps tiga.

What viscos engine oil do you use during the winter you should use a thiner oil than during the summer. just a thought!

Had same problem on mine, new battery made no difference, suspected overnite drain so left batt off, no difference, bought brand new starter, no more problem.