Mystery non-starting problem

[mookie32]

Hello all,

In the morning, I can start my 1985 300SD turbo, drive it 45 minutes to work, kill the engine & then restart it. I can start it at lunch, go grab some food & 45 minutes later drive it back to work. When I get ready to leave the office it won't start at all, not even a little 'click, click, click' of the starter to let me know the battery is dying. So I get the car jumped, drive 45 minutes home, kill the engine & then try to restart it & I get nothing.

The next morning I go out and start the car and it fires right up. I've been carrying around a portable battery jumping unit because I've worn out my 'free jumps' with all my co-workers.

Any ideas?