Peugeot 607 Terminal 30 Interrupted

I had something similar with my 607. Check for a voltage drop across the starter motor while cranking. I once chased a similar issue that turned out to be a short circuit. How old is your battery?

Voltage drop on the starter motor, got it. The battery is relatively new, but could still be defective, I guess. Where did you have the short circuit?

Mine was eventually traced back to the ignition switch. It was an intermittent fault, a real pain to diagnose. Best take it to a shop before you end up chasing shadows and replacing random parts.

Thanks for the advice. It turned out to be the battery, as suspected, but the garage found a parasitic drain too. New battery and fixing the power supply drain set me back 290€. Appreciate the help!