my 07 hammer just got her 3rd battery...
the last owner put a very cheap carquest (was 16 instead of the ytx20) battery in and im pretty sure it is right around a year old. i went with the yuasa for alittle more $.
take it somewhere and get it load tested, dont just check the voltage, mine was reading 12.50 but failed the load test miserably, it started the bike great 2 times earlier in the day, then boom, nothing.
i would still guess spark plugs first tho, they are cheapest place to start, even if yours are still new, nothing wrong with spares. i fouled mine out on the kingpin a couple weeks ago right when i got it. but my bike was full of old fuel, had been sitting, and somone had messed with the throttle to where you had to leave the enrichener half on just to get her to idle warm...
2007 Hammer S 100CI
S&S air cleaner, PCIII, SRVT clubs exhaust, Avon grips.
2006 Kingpin 100CI
stage 1, touring setup to come soon...nm bought a XC.
2013 Sunset red and black XC