Every morning summer or winter my car sounds like its not quite gonna make it. The starter cranks, really lethargically maybe 1 rev. Then the starter stalls for about half a sec, then springs to life again. Somehow the engine miraculously fires and it bursts into life. When I first bought the car I replaced the battery as the original was in there. The new battery gave me peace of mind but didn't help a whole lot with the dodgy starting. A VW Specialist advanced the timing (on VCDS) to the top end of the window as he said it should help starting (didn't seem to make a whole lot of difference). With no load the battery shows 12.72v, with the engine running but loaded up (headlights, heated window, blower, wipers etc) we see 13.4v. It has a 70A Alternator which I think is maybe a bit small but seems to be doing ok. I should probably test the voltage drop under cranking but the tests I have done suggest the battery and alternator are fairly healthy. I don't have an inductive ammeter, I don't have a drop tester and I don't have VCDS. Any ideas? Its a 1999 AHU Engined Ibiza.
What is the cold cranking AMP rating of the batt? As a even a small TDI needs a lot more to turn it over than a large petrol.
From a quick WWW hunt it looks like it is a bit low on CCA for your car. I think you may need 740 have a quick hunt on ebay and see what Euro Car parts would do you for a new correct / higher spec batt. I got one off them 35 delivered for my petrol mk2. Worth it for piece of mind.
Clean all the connections from battery to starter, also check and clean the earth strap and return path. If necessary fit another earth strap between engine and body (you can't have too many). Might also be worth stripping down the starter and giving it a clean out. If you can splash for a new battery, get the biggest that'll fit in the hole, both in terms of CCA and also reserve capacity - you can't have too big a battery.
I cant really justify a new battery as the old one is just over a year old. I think I may have a go at stripping the starter and cleaning and all of the earth straps (superficially the straps look ok).
Get a jump lead Connect it to the starter body/bolt/earth and run it back to the negative on the battery and see if it starts better If it does then its a poor earth path. If not then it could be the battery cranking amps as I`d have thought a 75 was the one for your car but it would be worth borrowing a bigger one to see if it was that
