I have a 2010 Ford Fusion and have been having starting issues. The first time I heard a clicking sound when I tried to start the car and thought, well it's the battery. We have had some freezing temps lately so there was some corrosion on the on the positive terminal, so I cleaned it. After messing with the positive cable and cleaning it, I noticed the interior light immediately came on; so I cranked the car, and it started right up. I stopped by a local auto store they checked the battery and it tested good, as well as the alternator and starter, all good. The guy put some contact grease on the terminals and some shims believing a connection problem was suspect.
The car ran well all day.
The following morning, same issue. I gave the car a boost and the interior lights came on immediately, and the factory alarm activated, literally as soon as the jumper cables were attached. Started the car, all good.
It seems as soon as the car is left alone for like four hours or so, the battery seems to not want to start and there's a draw somewhere, then it needs a boost.
I ordered a battery cable fuse block, amp box circuit breaker, hoping this will resolve what is hopefully a connection problem.
Has anyone had a similar, or same problem?
Help!

 

All I can tell you is an alternator can charge when running, but it can become a parasitic draw when the vehicle is not running. But there are many other possibilities.

 

There is a battery saver relay that is supposed to shut down everything when all the modules are allowed to go to sleep. Something is keeping a module(s) awake and it could be something like a defective module, or something where the vehicle thinks you are going to start it . Sometimes this can be found by doing voltage drop testing on some of the circuits or best using a scan tool to determine which module has the problem. Last it could be something that is left on. The clue here could be the interior light that comes on when sufficient power is returned to the system.