If it is not connected to a system that drains it then typically it only needs recharging two monthly, however being continuously connected to a quality charger will do it no harm. The big no no is to leave it discharged for anything more than the shortest period possible, the greater the level of discharge it is left at the worst the situation. I leave all my leisure batteries continuously on qua;ity chargers.
"Reportely" Adli are from the 17th doing their small "smart" charger which cost an unbelievable £14. If on a budget this would be quite good for your needs. [Best check they are selling them first]
If you are reasonably "flush" then you would do far worse than buying a CTEK 5 Amp charger[Google it for best pricing} but expect to pay three times the Aldi price. I have two CETKs for my expensive batteries but also two AldI chargers for less critical uses.