As far as battery life is concerned, any lead-acid battery should never be allowed to sit in a discharged or partially discharged state for any length of time. If you have significantly used a battery for a session, you need to put it back on a charger immediately after use--even a single night in a significantly discharged state will cause irreparable harm to the battery.
If you use a "smart" charger (such as the one sold with the Vagabond), you can keep it permanently plugged in, as far as the battery is concerned. It's possible for a smart charger to be defective, but that should reveal itself pretty early in the charger's life. It's also true of everything else, by the way, that you keep constantly plugged and turned on--televisions, phone chargers, et cetera. A sealed lead acid battery is more stable in the face of a defective charger than a Li-Ion battery is. It will bulge and smell, but it won't explode.
If it make you nervous to have a charger attached , you can attach an electrical timer that will periodically disconnect the battery from the circuit.