Hmmm,

So if you lock the car, the battery dies quickly.

If you do NOT lock the car, the battery is fine and does not die quickly.

Maybe the anti-theft system or whatever module that is connected to is dead?

Did you post this in the SL forum? You may get some more people to chime in.

__________________
2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)