Make sure that your trunk light is going off when you close the trunk. My 1984 300SD has a trunk light that stayed on all the time, running the battery totally flat within a few days. If you drive longer distances, your battery may not totally die, but you could still be losing a lot of voltage as the bulb burns all night. This is an easy check; open the trunk and see if the bulb burns your hand. If it does, it's been on a lot longer than 10 sec or so.
Lehigh Valley PA USA
73 Olds 88, 72 MB 280SE, 78 Datsun 280Z, 71 T-Bird, 72 Olds 88, 83 Nissan Sentra, 85 Sentra, 73 230.6, 91 Integra, 83 300SD, 91 Volvo 940GLE wagon, 84 300SD, 95 Subaru Legacy L wagon, 02 Mountaineer, 91 300TE, 08 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon all gone... currently
2007 Honda Odyssey Touring, 2011 Honda Odyssey Touring