First thing to check is the cleanliness and tightness of the battery connections, directly at the battery inside the bodywork. Also check the tightness of the rear frame ground (negative jumper terminal) under the seat. Warning! Do not loosen this connection, it is very difficult to retighten. If the battery connections check out, there are some simple tests you can run. First, charge the battery. The AGM batteries in the Spyder need a little more charging capacity than what Roger mentioned above, IMO. Use a smart charger like a Battery Tender. 0.75 amps would be the minimum I would use, and 1.0-1.25 works the best. The battery won't be damaged at 1.50-1.75 amps with a smart charger, but could be with a standard charger.
After the battery is fully charged, let it sit off the charger for a couple of hours to overnight. If it won't take a full charge, it needs to be replaced. After sitting, it should test at greater than 12.6 volts with a multimeter. If it does not, it won't hold a charge and should be replaced. I'd disconnect it, charge, the let it sit and test again though. Some of the earlier RTs had excessive parasitic loss through the audio system, that sucked batteries down quickly. Your dealer has a service bulletin on this issue, and can test your system.
The other test to perform is a load test. With a fully charged battery, hold the throttle fully open to prevent starting and simultaneously crank the starter. Watch a voltmeter attached to the battery. The voltage should not drop below 10.0 volts. If it does, the battery should be more carefully load tested, while disconnected, and replaced if faulty. Low cranking voltage can also be caused by a bad starter, hence the need to have the dealer test again.