Battery should have started the car after 16 days in conditions you stated. Test light may not be the best for checking parasitic drain. Use a digital ammeter in series with either battery cable. Mercedes clock should draw around 5 ma and if that's the only load should have started the car. You must have a drain much greater than that.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked