iPod Shuffle Battery Recharge Cycles

How many recharge cycles should I expect for my ipod shuffle before battery fails to charge? I have charged once or twice/week and in less than 18 months the battery will not charge. To clarify, the green light goes on indicating that the battery is charged, but the iPod will not play. I turn iPod power on, press the "play" button and the light flashes green then yellow, but iPod will not play.