The range on the remote sucks, that's just the way they are. Presumably you have the two remotes that came with your car, compare them to see if one consistently works better than the other. If it does, and you can demonstrate it to a dealer, they should replace it for you under warranty.
The battery in the remote is supposed to last for many years and is not intended to be replaced, although it is theoretically possible to do so if you are willing to break the remote open.