I just had a dead battery, used trickle charger all winter. Service manager says Ducati battery warranty is only 6 months.......ended up another $108 out of pocket, if this battery dies again by the end of the season, Ducati can kiss my business goodbye.
Don't know about the US but here in England we don't get much warranty on Batteries. My wife's car had a 3 year warranty and the battery failed after 14 months and they wouldn't change it (they said the battery only has a 12 month warranty), although the identical replacement they wanted me to buy had a 5 year warranty.
In the small print you will probably find that batteries are listed just above brake pads, clutch plates, drive chain, fluids and tyres as 'consumables'
my "new" used 03 999BIP had the battery replaced under warranty even though the bike is out - apparently DNA knows the 999 comes with a crappy battery. The battery was shot after the dealer delivered the bike - I called - a little later I got a new battery. Fight it out with DNA!