I went out to crank my car and the battery was completly dead. When sitting in my car I heard a clicking noise from under the hood. I looked in the fuse box and could hear the fuse box making a funny noise and could feel a vibration in it. I am stuck and do not know what this is or how to fix it. I jump started it and it cranked then I took off jumper cable, turned it off and it would not start again on its own. When the car was running I turned on the AC it it died instantly. Could it be the battery or alternator? Please help!!! 99' Mitsubishi Galant ES

Jump it again, but don't take the cables off right away, let it run for a minute, just so you know that it's running fine, and then take the cables off, if it dies now I can almost guarantee you that your alternator is bad.

Once the car is started, the car should still run even if you have a dead battery, because the alternator should be powering the car, and charging the battery.

You should charge the battery before you run the car with the new alternator though, since a completely dead battery is hard on a new alternator.

The average life of a battery is about 5-6 years, so if its older than that you may want to replace it at the same time.

put a volt meter between the terminals on your car and the voltage should be betweeen 13.5 and 14.4.
if its not its will be your alternator

Jump the car, turn off everything inside the vehicle (ac, lights, etc,.) Take off jumper cables while car on, now remove the negative cable from the battery only and if the car shuts off instantly its the alternator. It works, trust me...

let me know how it works

in all likelihood ur bettery is dead flat. if it's older than 5 yrs than buy a new one. best to go for super heavy duty. its worth the extra cash. jump it and leave ur car to idle for 15-30min to charge it up. check the cells for fluid levels(u can top these up with demineralised water which is fancy speak for clean rain water). ur car only uses the battery to start the engine and from there the alternator takes over. alternators usually only put out between 80-85 amps of power which is used for running everything your car needs (a/c, lights etc.) and charge ur battery. test that its working right by turning on ur accessories one at a time. start with head lights and high beam, hazard lights, then interior and map lights and lastly a/c. after charging ur bettery, if every thing works fine together then its ur battery. keep and i out for slight dimming in ur lights when u turn each accessorie on. if the lights dim each time u may want to have the alternator looked at.