How can I fix my Siemens CDR 2005 car Radio/CD player?

My Siemens CDR 2005 car Radio/CD player sometimes switches itself on to the last radio station played when the car - a 2003 Vauxhall Vectra - is parked. This is usually during nights and when the weather is colder.

I've also experienced a flat battery when leaving a CD in the player and switching off only by turning off the ignition. The remedy seems to be not to leave a CD in the player.