Batteries can last a year...or ten. Each one is different, depending on climate, charging type, charging frequency, vibration, whether the battery is ever fully discharged, and other factors. I suspect it also depends on the individual battery. Four years is probably about average for the Spyder battery...maybe even above average, although there are plenty of original batteries still running around in 2008's...like Nancy's.
Before you condemn the battery, clean and tighten the battery terminals (at the battery, under the bodywork, not at the jump start terminals under the seat). Check to see that the rear frame ground (negative jump start terminal under the seat) is tight. If that doesn't cure your problem, you can do a little testing if you have a multimeter with a DC voltmeter function. Check to see that the battery will take a charge by testing voltage after it is shut off immediately following a good road run, or immediately after it is removed from a battery maintainer. You should see better than 12.7 volts, preferably nearer 13.0 or more. To test to see that it will hold a charge, check the voltage again after letting it sit several hours to overnight. Voltages less than 12.7 indicate a weak or failed battery. You can do a crude load test by holding the throttle wide open to prevent starting, cranking the engine, and watching voltage during cranking. It should not drop below 10.0 volts. Also check the charging system. With the engine running at 4,000 rpm, check the voltage. It should be 13.0-14.0 volts.
