Hi zafar,----You may have "hit the nail on the head" with the blower motor running with key off. You have lost some "serious amps"in about 8 to 10 hrs overnight out of that new battery.Where there is amps (current) flowing, there is heat. With a cold engine, (overnight) & battery charged ,windows open & hood open,doors & trunk closed, listen for anything running,possible blower regulator with a "sick" transistor running at low speed.Also feel the rear of the alt for heat, possible a shorted diode. I use an infared temp tool , it works great for this test.If nothing is detected from the above checks,it's time for a DVM set on 10 amps (auto range) in series with the negative post & the grd cable. Read the amps or milliamps , approx .50 MA is normal current draw for modern cars with ECMs, body modules, radio (keep alive) & all modules have gone to sleep mode,usually after 20 mins. Start removing all fuses , one at a time, when the current flow drops down to normal, that last fuse you removed is the problem circuit.Now you know what "street" to go down, so to speak.That 600-800 amps is going out of them cables some- where, when you open the circuit with the fuse or possibly a relay, same deal, one at a time,from relay panel(rear of fuse panel),you have stopped the current flow & found your problem circuit. We know it has to be a circuit that is powered up all the time with the key off, so get a test lamp & write the numbers of the fuses that are "hot all the time", these are the ones that you are concerned with for now. Remember the only way to get to the bottom of this kind of problem is "Repairs through testing ", You have to fix it with " SMARTS NOT PARTS ". Please post your findings so all can benefit. Good Luck,----Ray