A lot of times, channeling energy into an item means that the energy is limited. In a sense, it is similar to when someone makes a sigil for a purpose. They will add energy to the symbol for its intended purpose -- which is typically single-use. The energy or effort you add to it may last, but in my opinion it is because of the mental connection, in a way.
Imbuing an object with some property, say protection, works in part because every time you put it on, you remember its purpose. So with that, you are continuing its energy every time you think about it. It starts with protection, and then you add good luck. You could probably think, "I've charged this for protection and luck," every time you don the necklace. Perhaps even three or four.
Eventually, however, the list gets a bit long. For some people, an item should have one purpose. For some, it can have more than one. It is a matter of belief and preference, so I will not dictate yours. My opinion, though, is that at some point your list could be long, if not at the least redundant:
"I've charged this for protection, good luck, monetary gain, traveling safely, loving friends ... or was that love in general? Any way, loving friends, guidance from my guardian angel, uh, I think some other things."
See? With such an exaggerated list, it eventually starts to lose its potency. As long as you remember everything, I think it should be fine.
Also, some people will suggest "recharging" the item on occasion, sort of to give it a refresher. It will, at the least, help renew its purpose to you, and make sure it is topped with the intended purpose(s).