If you can drive to your closest service station, have them do a load test on the electrical, that will tell you whether it's the battery, alternator, both, or neither. If you can't drive it, start with the basics of trouble shooting..... do your dome lights come on when you open the door? How 'bout headlights? If you have a meter, just check the voltage on your cig lighter with the engine off. Then check it while starting the engine.... does it dip drastically under load? It should not dip below 11, and then at high idle (if everything is good) it should jump to 14. Any further questions please post them, and I'll try to guide you through the best I can. Oh, yeah... it would help if I knew your year, model, and mileage.