[Diesel_Dave]

I don't think there's a problem with your car. I suspect the problem is actually fairly straightforward. Your engine isn't on long enough for the alternator to recharge the battery.

The starter takes a fair bit of power to crank the engine. This power comes from the battery. After starting the engine needs to recharge the battery via the alternator. If the engine only runs for a short period of time the alternator hasnt restored as much charge as the starter consumed.

This almost happened to me a while back when it was really cold. Even though I typically bump start I noticed that my battery got really low one day when it had been dark a lot and I had to use my starter much more than usual due to some mistimed lights. Since it was dark and cold it takes much more power to crank my diesel. I made sure I bump started much more as opposed to using the starter for a few days and then it was fine.

If I recall PaleMelanesian has had the same problem even though he bump starts a lot.

So my guess is you either have to keep the engine running more or put the battery on a trickle charger at night.