2004 Ford Expedition Battery Problems

I had my battery checked and the auto parts guy said that the battery had 80% life. But car still has days when it will just click and not actually start. Of course all I need is a jump but I have also had the battery terminal replaced and still having the same problem.... My husband cleans the (i dont know what you call them) "the connections" i guess, regularly so that they dont have build-up. But it's getting pretty annoying to deal with.
Thank you for your help!!