Well, I believe they make a actual battery charger...but battery tender junior isn't really a charger.
As far as your problem, I would suggest getting a new battery! If you want to ATTEMPT to bring your old arse battery back to full charge use a full blown car battery charger, then a battery tender jr to maintain it.
However, I say everybody should change their bike batteries every other year! Reason being that bikes don't have alternators. They have stators, which is a newer version of a old school generator. Basically they SUCK goat nads!! And by doing what I'm talking about, keeps you from being caught at the store with a dead MC batt...
Get a new battery and a battery tender junior...then you'll be good!! I'm Gas Man and that's it!!