When I bought My grand voyager in 2009 I had this very same problem, the issue I had was the battery that was fitted was a trickle charge battery, my daily journeys where 15-20 mins this wasn't enough to charge the battery I spoke to Chrysler assist and they replace it with a fast charge battery, I have since replaced the battery again recently but didn't use Chrysler as they wanted £475, forgot where I got it from but will look cost £166 still a lot for a battery but didn't need to re-mortgage hope this helps