a dumb charger will charge your battery to a fixed voltage and continue to deliver a charge -even if its a trickle charge. This kind of battery can shorten the life of a healthy battery. Then, eventually, when the battery has lost it's capability to take a charge, the continuous charge current may start to create some serious heat problems. Heat shortens your battery life.
a slightly smarter charger will charge your battery to a fixed voltage then turn itself off. This fixes the problem with leaving the charger on the battery and creating heat.
a great charger for battery storage, but totally unecessary for day to day use, is a battery charger similar to the 'Battery Tender' product, when it has completed its charge cycle, it switches into a float charge mode. Where the charger will continue to top up the battery as needed. This is a good way to store a motorcycle battery for the winter, cuz a typical motorcycle battery will loose as much as 5% of its charge per month.......most batteries that are stored for 3 to 5 months could benefit from this kind of charger, cuz the battery may discharge to deeply without it.