[Full_Spectrum]

What is the voltage of the battery? Using a multi-meter, get a voltage reading from the battery. You can put the probes into the tender leads for this.

Get the reading when the bike has NOT been on the tender for a few hours.

That should tell you if the tender is actually working, and/or if the battery is dead.

 

[Full_Spectrum]

Just because the Battery tender has a green light means nothing. It can't detect weak battery cells. I have had batteries last eight or more years on a Deltron Battery tender. Every battery that I have had fail after many years had a bad cell. The light was green on the charger. Batteries don't last forever no matter how good you treat them.

The resting voltage can tell you something but its really not as important as when the battery is under cranking load. Connect the battery to a voltmeter. Read the voltage while you push the starter button. If the reading drops below 10v the battery is bad. It has a bad cell or cells. That's also why it's not taking a full charge. Even if the light is green. The charger doesn't know any better.

Correct. That is why you leave the battery off tender for a few hours.
With a bad cell/collapsed plate/whatever, resting voltage will fall to less than 11 within an hour or two, meaning the battery is scrap.