a battery begins to lose it's charge as soon as you remove the charging current. once a battery starts to lose charge crystals start to form on the plates which in time will limit the charge that you can put in. trickle charging is designed to hold this at bay - it won't stop it entirely. (all is not lost as batteries can be recovered (to some degree) though it's a involved process better left to a battery specialist - you could do it but you need more gear.)
most simple chargers are preset to supply a specified charging current then cut-off when the battery is fully charged. better ones reduce the charging current to a sustaining top-up level - a trickle. once again all is not lost, always charge the battery as soon as possible after use and always before storage. if you don't have a trickle charger or can't leave it connected all the time put it back on charge once a week but not less than once a month.
(two/three things here -
a golf cart battery is NOT the same as a car battery - they are built differently and definitely have different charging requirements. they are also used differently, a car battery is high current/short cycle, a golf cart battery is designed for sustained use, 'deep discharge'.
different types of battery require different charging methods and different charging currents, the charger you got with a lead acid golf trolley battery is no good for a gel battery. the lead-acid battery probably charges at around 2.4 Amps but will be higher (around 3 or 4 Amps) for Gel and different again for AGM. A car battery charger will typically charge at 5 Amps or more - not advised.
sealed batteries NEVER fully charge - they are designed not to. the charging process produces gas, a 'sealed' battery can't vent it so don't charge as high.
