A/C is the biggest electrical consumer ranging from 40 and above amps...next is the radio (lalu na kung fancy sound system), the rest of the electrical system is somewhat we call "manageable" levels.

well the starter is another issue, no doubt na ito pa rin ang pinakamalaki sa kailangang amperahe. what i mean is when the car is running....

with regards sa problem, check the battery drain...with engine off and all electrical systems off, remove the ground cable (usually negative) and connect in between the multitester and switch it into milliampere (mA)... cars with aftermarket alarms usually consume 50 -100 mA...some consider more than 50 mA as abnormal...

it is always better to have it checked by an experienced and reliable auto electrician but check the easy things first like battery voltage and age, fluid levels, ampere check, loose or corroded connection, visible stripped wires touching other metal parts of the car and so on before you go out sa mga shops.