I cannot agree more with Nancy's Toy and HarryPottar's observations on battery charge and flooding. Here's my experience, which should sound familiar to CamdenLake
About three weeks ago I allowed my RT-S to sit out under its cover for 10 days without starting in the mid-upper 90 degree heat. Super hot weather is just as hard on batteries as super cold weather. So ...
I go out to crank her up and know the battery is down to about 65%. She cranks nice but won't start. One could smell the fuel as it cranked. Would not start. I think the original poster mentioned something about turning the throttle grip wide open. No, that won't work. The Spyder throttle control is electronic. It does not kick in until the vehicle is started. A temperature sensor opens the throttle automatically when the ignition is turned on. The throttle grip trick only works on throttles with mechanical linkage to the throttle body.
All cranking the Spyder with a low battery (below 80% or so) does ... is run a high potential of flooding it. Once flooded, the Spyder is quite difficult to 'unflood'. After my efforts to start the Spyder were fruitless, I left it overnight on a tender. It took all night and half the next morning to get the battery to a full charge. So then I go to start it ... which was still difficult (because it was still flooded from the previous day). Finally, it caught ... the engine ... barely getting going with a puff puff puff bladda bladda bladda and a knocking sound. If one tried to rev it it would die. Ultimately, I started it again, and just let it run until completely warmed up ... Gradually, the excess fuel dumped through the system, everything smoothed out and all was fine.
All this because I let the battery get a little low. Keep your battery on a tender and try not to let it go below 80%. Otherwise the electronic fuel system will dump too much fuel into the throttle body / injectors, there will be insufficient spark to kick the engine, and you will flood out. I have had the Spyder on a tender ever since this incident and had no further problems.