I AM having problems starting my car sometimes

I AM having problems starting my car sometimes. I am unsure if it is the alternator or the battery is at fault. If the car isnt sufficiently* warmed up then it dies after I have come to a stop somewhere. It turns over but if I come to a stop sign like recently or just stopped somewhere for awhile and then get back into the car and go like at a convenience store then sometimes it wont start. The other night it stalled on me at a stop sign after I had started it after it sat for a long time while I was at a church service. I didnt give it enough time I guess to warm up and then when someone tried to jump it off from their other vehicle it still wouldnt but after I got it back to the church(4 guys pushed it back in reverse) and tried it once more it still wouldnt start. Then a guy got in my car turned off the heater which I accidently left on and then they it started right up. So sometimes it seems like it is the drain on the vehicle, or not sufficiently warmed up, or maybe even a battery problem. I got the everstart battery in october of 2011 but here in tennessee it has been colder than normal and much hotter than normal so I dont know if it could be the alternator not charging the battery enough or the battery itself or something else or the ground cable from the battery not the positive or the neg cable or if it is just could be due to the corrosion. I dont have a clue and I have very limited in the way of finances so I dont want to spend money on a part if that isnt really the problem. Now I do have an OBD-II meter that I bought for christmas for myself but I also read that those things wont pinpoint the exact problem so would using it help me at all at this point. Any information you give me would be appreciated. Thank you