Hybrid vehicles do appear to be more susceptible to flat batteries, although five weeks is a relatively long time for any vehicle to be left unused. If you plan to leave it parked up for extended periods in the future, you may wish to consider using a trickle charger, like this one from CTEK - kit.honestjohn.co.uk/reviews/review-ctek-battery-c.../ If your car has keyless entry you may also wish to consider moving the keys far away from the vehicle when parked or using a Faraday bag - this prevents the vehicle from constantly scanning for the key fob, which can create a drain over a period of time.