The issue is more likely the charger. 3 year old batts tend to stay low during the charge, and the tender doesn not offer enough beginning current to shock the cells to really ionize the electrolyte and remove the sulfation,, they just don't.
If you stuck that battery on a conventional, non-automatic chargere, set at 2 amp cycle, for 2 hours, it would charge, and you would be able to monitor the progress on the meter (actually you HAVE TO montior, being a manual charger). You then will get a full charge. I went thru this during my spring ritual, when my batt was uber low because I left it in the bike all winter in a frozen garage. It was the second season on the batt, and winter prior I did have it on the tender in the frozen garage for 50% of the time (mistakenly shut it off a few times, due to the circuit I had it plugged into..my bad). It came thru the first winter fine, not so on the second one. I could not bring this new bat back up using the tender, even after a week... 2 hours @2amps, and it was back to normal. Jumped the shark on that one, but I'm sure I took a year off that batts life expectancy. This was a C14 batt by the way, bigger than C10.
For C10 I found the Odyssey the best all around purchase, never had it on a tender, and it lasted and was in the bike, working perfectly after 6 full years when I sold it
