Computer lights on and Car shut down

The problem started when my car suddenly shut down when slowing down, I changed the fuel pump and everything went good, later on I've had problem with electricity as the battery went empty after leaving the car without move for 2 days, I changed the battery with new batteries 2 times but still If I the battery is going empty when not starting the car for 1 day, I checked the Dinamo and it is working very good, also I let the electrician check whether there is electricity shortage but he said nothing is wrong and no shortage.
Today my problem is : the light of computer goes on and the car straggle (like as there is a dirt in the fuel)and the RPM goes below 500 then suddenly shut down.
I tried to press all door widowns bottons together and I noticed that the electricity went low then then RPM less than 500 then car shut down.

The problem is nobody have the electrical divice which check the computer near me and I feel all repair poeple are guessing and waste my money for nothing
Please please help