Well you don't need max hapiness to evolve zubat, you need it to evolve golbat.
If you do what Trachy and I said in the recent question, "How do I get my togepi to evolve" then you can make your pokemon happy. It is just an added way to make your pokemon evolve. The more good stuff you do for it, mesages, sooth bell, keeping it alive, power drinks, and amity square, will raise its happiness.