Steering column circuit

Hi - I have a 2001 Caravelle 2.5 TDI which I have left unattended for quite some time. The battery is now flat and so when I have tried to jump it/charge the battery I am getting nothing (no instrument lights )After looking at the fuse box I noticed a cap on the underside of the steering column with a picture of the engine. This cap had popped open to reveal what looks like a fuse/circuit. A. What is this & B. with me putting a battery charge on the battery could i have blown something?

That cover is where the diagnostic port lives on later ones.

Under there is just a wiring harness for the ignition lock, stalks, and airbag.