When you "lose" your electricity, does your car crank? If your car does not crank the starter right after the problem occurs then it is most likely the battery or the cables which attach to it.
If the car will crank, but you get no electricity elsewhere, you should check the Smaller red cable off the + terminal of the battery, which goes to a distribution panel. The panel is on the left fender, just behind the silver relay. If you pull up on the outer panel of the this box it will slide off and you can check for corrosion.
If OK check cable which goes from there thru firewall to fuse panel.

A VOM ($20)will help in this endevour.
--
744 & 745 16v 4+OD, 245 SE auto, 242Ti 4+OD, 245DL auto parts car