to be even more specific you need a charger (they are ALL chargers) that only puts out 1 amp or less AND is automatic such that it will reduce the charge voltage and current once the battery is charged while monitoring the battery so it can continue charging again when needed.
there are several options out there, but the best is generally the battery tender and battery tender Jr.; both made by Deltran. For our small batteries you should use the Jr since it puts out 0.75 amps vs the other's 1.5amp.
And both of those units can be used to charge a dead / new battery and then left on there indefinatly to maintain the battery for long storage. I have used my BT Jr to charge my car battery overnight. The slower the charge (read small charge current) the better it is for the battery's health.
Remember, they are all chargers, just some of them will turn themselves off once the battery is charged and will monitor the battery (aka tend) and turn themselves back on / kick the voltage back up when needed.