I had to get a jump yesterday to start my truck (2000 Ford Explorer). I stopped by O'Reilly's but they couldn't find anything wrong. I was told to go to AutoZone to have the battery, alternator, and starter checked. I think it's the alternator. It didn't make a clicking noise when I went to start it and all my lights come on fine. Suggestions?
If you have a multi-meter, get the truck started then take a voltage reading at the battery posts. You should get about 14 VDC with all your accessories off, about 13 VDC with all your accessories on (headlights, heater fan on max, rear defrost if you have one). If your voltage reading is lower than that, your alternator isn't charging your battery.
If your voltage readings are fine, turn the truck off and immediately take a voltage reading of the battery. It should be above 12.4-12.6 VDC, if it's lower, your battery isn't holding a charge.
The first thing to do is check if all battery connections are clean and tight. A connection that is intermittent can be the problem. Rarely a cable can be corroded inside the plastic cover and not making good contact. ( My 98 GMC died a few times on the interstate ,caused by a bad battery connection.)