Thought you might want to know this.

This weekend I was driving my 1992 965 to the coast and stopped for a burger somewhere. When I got back in the car and turned the key... nothing. All the electric stuff worked fine, but the starter wouldn't budge (only heard a tick). Luckily, my dad was in the neighbourhood, so he came to my rescue. First, we thought the starter itself was stuck, but then we used my dad's battery and my car started right away.

Later on, I saw that my battery was actually too small for my car (only 250A) - some previous owner must have thought it was enough. So I bought a new battery, with a suitable 650A.

I haven't seen anything that could predict this. There was no warning light. All the lights worked fine, the electric windows and roof were OK, and the car always started immediately.
I only had some problems with the central locking, but I thought the batteries of the remote were to blame.