I bought a duel purpose one from halfords,it charges car batteries as normal or you can flick a switch and it charges leisure/motorcycle batteries,cost about £25-30,once battery charged it goes into trickle charge mode.I leave it on all over the winter when battery off van.Going into 3rd season with original battery and seems to be fine up to now.
Hi Lucy get a leisure battery charger that charges the battery in stages. They are a bit more expensive but i have found that leisure batts charged this way power a hell of a lot longer.