There's not much you need to do to keep your battery performing as it should, but a trickle charger is a must if you winterize and store your bike for the winter in your own garage (if you take it to the dealer, they will plug it into a trickle charger) to make sure your battery survives the winter.
Your motorcycle doesn't have an alternator that works the same way your car does, so it's not continuously re-charging your battery to full every time you ride. I'm convinced plugging your bike into a trickle charger when you're not riding it is a good practice to get into and once the bike cools down from a ride, I usually plug it into the charger. And, all the bikes are plugged into a charger right now.
There are lots of trickle chargers available, but I started using a Deltran Battery Tender a few years ago and have been happy with it. Like any of these chargers, when first plugged in, it brings your battery up to full and maintains full charge (without over-charging) as long as the charger is plugged in.
It comes with both a set of standard clamps or will allow you to attach to the battery posts with a lead to a quick connect attachment on the charger. This is how I've connected to the battery on both my Road King and Sue's bike, but I'm using the standard alligator-style clamps on the Buell.
I also like how I can quickly remove either connector from the charger which makes it easy to plug in whichever bike happens to be on the lift at any given time.
I recently added a new Battery Tender to accommodate for Sue's bike, but the only difference seems to be cosmetic to the design on the front of the case. Otherwise, all three seem to work the same. This maintenance tool has earned a permanent place in my garage.