Not necessarily.
Buy it now and store it with 50% charge. Every couple of months put it in the phone, see where it is, charge it to 50% and put it back in the box.
Yes, it will be down a bit -- like 1-2% -- in a year or two. Big deal. You won't even notice it.
Put AccuBattery on your phone. Set it to alert at 80% charge. Pull the phone off charge at 80%. Your battery will last 2-3x as long as normal this way, as it will only take about 0.2 cycles of damage being charged to 80% instead of full.
A good battery now, treating it this way, and one replacement and you'll make it to five years easily. If that's not good enough to the point you'll want something else for the expanded bands that carriers have opened up in the interium THEN start worrying.