First,....how old is the battery???
If it is dead, and more than 2 years old, you will be best off buying a new battery. Stick with HD!!!....they are a LITTLE more pricey than an after market battery, but MUCH MUCH higher in quality. HD uses AGM style batteries (Absorbed Glass Mat), they come pre-charged, and if PROPERLY maintained, they will last 4-6 years. Old style, lead acid batteries will only last about ONE year. Fuel injected models NEED AGM styles batteries, the injection systems will not function properly on lead/acid batteries.
AGM batteries REQUIRE.....SPECIAL charging procedures...DO NOT use a standard auotmotive charger...and DO NOT use ANY type of Load Tester, you WILL destroy it. The tester used on AGM batteries is about $1500....HD is the ONLY place that has the proper eqipment for test and charging DEAD AGM batteries..........take it to HD and let them test and charge it......or just buy a new one.
INVEST IN A BATTERY TENDER!!!!!!!!!!!!!!!.........you can get one from HD with the battery for about $60. It is a STORAGE charger that comes with a small "pigtail" that bolts to the battery and a samll charging unit that plugs into the wall, the Pigtail will plug into the charger unit. Whenever you are not riding the bike, KEEP THE TENDER PLUGGED INTO THE BIKE......it will ALWAYS keep the battery fully charged.......this is a must for cold weather storage!!!
Get a new HD battery and a Battery Tender, follow my (and the dealer's) instructions and your bike will always be fully charged and you will not need another battery until at least 2014.