Had a quick google and came across some caravan forums and they say that charging a lesiure battery with car charger could be risky .
As if you do not disconnect the charger from the battery when fully charged the leisure battery could release gases . And a Car battery and leisure battery charge at different voltages and go through different cycles when charging .
Possibly dangerous and it will kill your battery far quicker also some info suggests that a leisure battery should not be fully discharged and should be charged when the battery is 50% discharged .
Hope this helps Dazmond

. Mike