Which year? Ours is an '06 Sun Ti on a Renault Master chassis, so these comments only apply to this model. I had various problems with ours when I first got it - a mix of not knowing how to isolate stuff and (I think) old knackered batteries. I replaced both the engine and leisure batteries and have had no problems since.
First off, make sure the big red keyswitch next to the Calira charger under the bench seat in the ON position, and that the main on/off switch and aux switches on the control panel by the door are all ON.
Are you getting any charging lights on the Control Panel?
If not, then the Calira chargers (under the bench seat) have been known to pack up - you should be able to check whether it's working using a multimeter.
There are schematics of the Calira connections on my website here: http://www.morphology.co.uk/knaus
if you're no good with a Multimeter, you may have to call on an Auto Electrician to help you out.
If the Calira has blown (which I sincerely hope it hasn't), then they can be a bit expensive to replace, though there is a place in Wales that will repair them: http://www.atlanticmotorhomeservices.co.uk/
or sell you a reconditioned one.
When I let my leisure battery go flat, when I started the engine, it blew a big 40A inline fuse that is located next to the Engine battery under the access panel between the cab seats. That took me a while to locate!
Our leisure and engine batteries go flat in a couple of weeks even if I try to ensure nothing is drawing power - I think the immobiliser runs it flat all by itself - so now I keep it permanently hooked up to the mains (which I can do, as it's on my drive, though this may be more difficult if yours is in storage). This doesn't seem to have affected the leisure batteries, as the Calira seems to be one of those so-called "intelligent" chargers which cycles the leisure battery without cooking it.
You may need to consider adding solar panels to keep the batteries topped up whilst in storage if mains hook-up isn't an option.
It is also worth posting your question to the Knaus Owners Club forum: www.knausowners.com
there's a wealth of knowledge on there.