Why my car is loosing electrical power and yet I changed the battery a

Do you have any electrical add-ons such as an aftermarket car radio? It sounds like you may have some sort of parasitic draw coming off the battery that's draining it.

With the car off, disconnect the positive battery terminal and insert an ammeter between the battery and the terminal. You should see something on the order of not more than 50 milliamps (some cars can go as high as 85), but anything more than that means something's eating your battery.

Go to the fuse box(es). Pull them one at a time and watch your ammeter. You'll see a major drop when you find the fuse or relay feeding the parasitic draw. When you do, trace the circuit and see what's on it; something there will be your culprit.