I have a 56 400h and have learnt the hard way not to use any electrical devices (radio, DVD, etc) on the car unless the engine is turned on (although it may not actually be running). I've had the car for four years now, the battery under the bonnet loses power to start the engine very quickly ie the READY message is not displayed and tells me to put the gearshift in P to start even though it is.
Also if I go away on a business trip, then i have had the problem after three or four days leaving the car standing.
I don't know if this is the original battery, but suspect it maybe so I think this battery needs to be replaced as the loss of charge seems to happen quicker (twice this month) now.I have not had any issues with the main power pack which contiues to run well.