My Car has been sitting for 4 months in negative temperatures. I brought the battery inside but it doesn't seem to be charging and it won't start the car (it'll turn the motor over a few times very slowly). So i grabbed the battery from my mom's car which has 1000 CCA's and that started my car fine. Now i let the car run for about 5 minutes and then disconnected the negative cable for the battery and the car quickly died. I'm pretty sure that the alternator is supposed to keep the car running with no battery but i could be wrong. Do i need a new alternator as well as a new battery?

 

you very well could need them both. since the alt's so easy to get at just take it off and take it to autozone or somewhere, have them test it.