I just replaced the "new" battery, that the guy I bought my bike from at the end of February had just installed, with a Motobatt MB16AU battery and I can tell a huge difference in the way it starts. The battery he had put in it was one of the cheapo UB16AL-A2 ones.
I think the stock R/R killed it. I replaced the R/R and tried to repair the battery with the genius battery tender but it wasn't meant to be. It would give me 2-3 starts but after that it was the dreaded click of death. If I didn't have the choke on when starting cold and had to give it a couple of attempts, it'd croak and I'd have to hook up the battery tender. I didn't like the fear of being stranded either.
The new battery is an Absorbed Glass Mat battery, totally sealed so I didn't need to hook up the vent hose to it. Came charged out of the box and it really turns over the bike with ease. I recommend it highly!