Won't start
 

A few days ago I drove my expedtion to my babysitters house before work. It started up and drove fine there, but after turning the car off and going inside for five minutes, it barely started back up. Turned over slowly and the radio and gauges didn't work. I made it the half hour drive to work, turned it off, and immediately tried starting it again. As I suspected, it wouldn't start. Just made a fast clicking sound. My brother in law came a few hours later and said the connection was lose on the battery post. He messed with it and we were able to start it. It started again a few hours later when I got off work but barely made it back to the babysitters. There was very little powet- no radio, windows wouldn't work, no gauges, etc. It would not start again after turning it off at the babysitters, even after messing with the post. My husband put a new alternator in. After jumping it, it ran great. I drove it to the gas station, turned it off to get gas and it started right back up. It took me all the way home, about a half hour drive, with full power. That was yesterday. Today, I go out there and it won't start and is doing that same fast clicking noise. My husband ready put a screw to tighten the battery post connection but I tried moving it around anyway with no luck. What could be causing this? I thought bad battery, but it didn't make sense to me why the power would be so low after starting it the first day, since the alternator should have recharged it. That's why we replaced the alternator.

Before we do anything we need to confirm that the battery is good.If for instance, it won't hold a charge, replacing the alternator will not help.
If the battery is defective , replace it. If it passes the checks,all the cables and connections need to be in good condition and clean and tight.
Unfortunately, these days, just because the alternator was replaced is no guarantee it is working properly. It's output needs to be confirmed. Some places will test them for you. If the battery is OK, and the alt is confirmed to be working properly, and connections are good , the vehicle computer which controls the charging system in some vehicles needs to be confirmed as working properly. At this point we don't know anything about your vehicle, except it has a problem. They are all different and it is important to know , year, model etc.