In case anyone else gets the problem. On my car the lighter socket is powered off when ignition is off so when I start the car the Mini 0805 also starts up. Problem I was getting was that on starting the car I got repeated startup chime (triple chime) sometimes it would stop after a short while, sometimes it would change after a while to a noise not unlike the noise a stuck CD makes on playback and sometimes it would just keep repeating. Replacing the internal battery cured the problem. This is not uncommon in electronic kit that holds programming in memory. The battery is charged by a very simple charging circuit and is used to retain power to the memory when the power is turned off. When the battery fails it has a low internal resistance. When the power is on power is supplied to the battery but the low internal resistance drags the voltage down below what the memory requires to operate so you get erratic behaviour. Elsewhere on this site are dismantling instructions, I got the replacement battery from China via eBay and it was a 2 minute job with a soldering iron to fix it.