Car Won't Start, but Will Jump and Run. Turn Her off and Dead Again.?

so its late and my car is being a douche. figured i'd ask what could be some issues to try and troubleshoot my self before i pay a butt load for something silly.

92 mazda mx3

car has been running fine, then i took it to a bar to watch the fight (great fight by the way) and when i came out the car was dead. i thought i left the lights on (i do this a lot) so i pulled out my trusty jumper cables and got her going. it took longer than usual to jump like the car was sucked dry (not typical). got her running and drove home. while i was driving my lights dimmed a few times so when i got to the house i left her running for like 20min w/o the lights on to make sure she was charged fully. i just went out there and turned her off, waited like 3min and turned her back on and she is DEAD. not even a noise, sucked dry again.

so there is like a butt load of corrosiony white crap where the battery thingies are (so technical right) so i assume i need to get that cleaned off as its not helping. but if that doesnt fix her, what else could it be? a new battery? the starter? some other magical thing i've never heard of that's sucking the life out of my beloved hoopty???? help please and thank you

Suggestion:

pls clean off the battery terminals (not thingies lol) before you proceed any further. corrosion can throw a diagnosis right out the window!!!! do your lights work when the car is not starting?

to me it sounds like you alternator may be on its way out, its not very magical. the alternator simply takes over for the battery after the vehicle is started and supplies the voltage to keep the car running. starting the car is the single most strenuous job for the battery and that is why your car cant start on its own but when jumped it will start right up and the battery is keeping the car running but it it wont last very long since you said that your lights were dimming.

it isnt recommended on newer cars because it can damage the computers but you car will be fine with this backyard mechanic alternator test…. start your vehicle (even if you have to jump it) go to your battery and disconnect the negative (black) terminal, if the car dies then your charging system (alternator) isnt working properly. if the car continues to run then your alternator works fine.