What is a trickle charger?

That would depend on the amperage of your charger but as a rule, slow cgarging at low amps is better than fast charging at higher amps.
If you're having to recharge more than you like, get yourself a trickle charger and use it as needed.

I have a 1 amp charger that I will leave on for up to two weeks if my battery is low enough that it won't turn the starter over.  At that low rate you don't have to worry about boiling off the water in the battery.  Harbour Freight sells some cheap float chargers that will vary the amperage down to almost nothing to keep your battery fully charged.  Plus my Predator and my DR650 both use the same size battery, so if need be, I have a standby!!!

what is a trickle charger

A trickle charger is a charger that charges at a slower rate. Often times they have a float feature that senses when the battery is charged and drops the amps untill it senses a discharge and bumps back up. This works great for off season battery storage and in some rare cases can bring dead batteries back to life. Battery Tender is a good brand as well as Christie brand chargers. I picked up a generic one from Walmart for around $15 and it works good.