We are the Lone Star Voyagers a chapter of the American Voyager Association. This open forum is for the members and guest of the LSV-AVA. Please feel free to use this service. Remember this is a family riding chapter.
Have you checked the voltage of the battery with a VOM? Some batteries are bad right out of the box.
If the voltage is below 8 or 9, an automatic charger (like the Battery Tender) will not charge it. This doesn't mean the battery is bad, it just means the voltage is low. Use a manual charger (an old-style one that has some sort of timer on it that you set), and charge it for a couple of hours, then check the voltage. If it's over 10 or 11 volts, put the battery tender on it to finish the charge. If it isn't, put the manual charger back on it for a couple of more hours. HINT: put your meter across the battery poles before you shut off the manual charger, and watch what your meter does when you shut off the manual charger. If you get a rapid voltage drop of more than 2-2.5 volts, then chances are there is a shorted cell and the battery is bad. Even partially charged, a good battery will drop less than 1.5 volts when you shut off the charger (this is called 'surface charge' , and a 1 volt or less drop is normal) If it checks good, just connect the battery tender, and let it finish the job. (NOTE: an 'automotive style' battery checker will not work accurately on a small motorcycle battery.)