I have had a 2008 Challeger now for 18 months, during this time i have had a lot of problems with flat batery. I bought a new one in Feb on the dealers advice.
Having suffered the problem all summer, the dealer agreed to test the battery again, however i did some digging to actually find that there was no charging voltage at the battery.
to cut a long story short, not only do you need to have the charging switch on in the cupboard but also the switch on the control panel and the caravan battery switch. It appears that a number of owners i have spoken to do not know of this and there is no mention of it in the handbook.
This appears to apply to 2008 and 2009 model year