i got an w126 1989 300se and i changed the battery 5 months ago and i changed it again 2 weeks ago .. and if let the car set for 2 days the car wont start and no power going on.. and my central lock stoped working too.. today i jump started the car in the morning to go to school and when i came out it was dead .. but few hours later it started fine.. any body knows if all or any of the w126's has a battery cut out switch or anything..

 

There is no battery cut off switch and could be many things, vacuum pump for locks, trunk light, door light, power antenna or short in your electrical wiring. Connect amp meter to battery with engine off and doors closed and see how many how much current is flowing out of your battery to determin what it could be.