HI
All modern smart charger are ok to charge the battery with it still connected
I use a Jaguar CTEK charger and these can be put on and left on long term
mine has a special socket in the boot for plugging the charger in, without the need to expose the battery
the only thing I would recommend is most of the jaguar batteries have a vent tube from the battery to somewhere out side the car, so no buildup of gases, hydrogen in the case of most batteries, so when disconnecting the battery charger, make sure you switch it off at the mains first, as not doing this can create sparks on the clips and if there any build up of charging gases, it can't do any damage
cheers
Joe