Hi and welcome.
Regret I cannot help with your specific query as I don't get mine until tomorrow, and it's a petrol!
On other vehicles I have seen aftermarket stereos, alarms, and feeds for satnavs/phones taken direct from batteries, though I am sure it's frowned upon.
Hope you enjoy it!
2008 model 1.8 petrol C-Max Zetec in Avalon Blue - arrived 14 May 2011. Also own and drive: 2005 Mercedes Benz SLK350 and wife\'s Fiat Panda 1.2 skydome.