battery died id car sat 4 more than 10 hrs not battery not alternator mechanic had car 3 weeks and returned it wmseveral disconnected features saying it was only way car would function something staying on that drained battery $1300 later car doesn't die but have no radio, cd, & some idiot lites disconnected..no sound on alarm, etc. can this be fixed? did i get ripped off?? mechanic said place where all wires connect was rusted, and i did drive car partially under water during squalls 2 years ago. advice?

Exactly what got wet on your car, most of the times you replace this and the batt leak will go away. some modules need reprograming so you need to know what it is before you change it. try cleaning it with contact cleaner and read the codes with a scanner for bmw that lets you enter the modules that are not working correctly.

Making better decisions will be your best bet here. DO NOT FJORD WATER UNLESS YOU ARE IN A CAPABLE OFF- ROAD VEHICLE. And find a better mechanic. That would be a good start. The e39 is a hugely electronics driven vehicle. There is whole volume dedicated to JUST the electronics from Bentley Publishers. I would recommend parting out the vehicle.