Charging batteries

The camper van has been sitting parked under its "hat" since early November but soon it will be out on the road again. The batteries need to be maintained because their charge leaks away as time passes. I'm not sure how old they are but they definitely aren't new!  Last year I ran the motor for about 30 minutes every three weeks or so but this year I'm using a more advanced battery charger to do the job (Seems slightly better for the environment). Now and again I switch it between the motor battery and the leisure battery. Just now it's on the motor one and the reading is "Storage", which means it's pushing a small trickle in as when its tiny computer says it's time. The charger is positioned so I can see what is happening through the window, as it's a slight faff getting into the van when it has it's winter hat on. When I return from the Pyrenees I'll switch it over to the leisure battery. Soon after that I'll hopefully remove the cover and the solar cells can start doing the job for me.
Tomorrow I take the train down to Arlanda (Stockholm) Airport, ready for an early flight Sunday morning.