If you have a voltage meter, check the voltage with bike not running. Turn on headlight, do not start motor, wait for two minutes, turn off headlight and check voltage again. If it drops significantly from first reading, your battery is suspect. Laying on it's side like that could definitely drain the electrolyte. Have you checked to see if water level is low? Top off with distilled water if not too low, put it on a battery tender, then repeat the battery check. A fully charged battery should show 12.8 volts or more, not running, after headlight on, and checking again it could drop into the 11 volt range, and that would show weak battery condition. I would want to make sure my battery was in excellent condition before doing any long range riding. Take into consideration the age of your battery , and replace it if there is any question in your mind. It's the heart of your bike, keep it healthy!
Alfego