I disagree Alain

The electronics that you design-in between the PIC and the incomming Power Source, be it vehicular or Battery sourced always ensures the PICs supply is clean. If it's not, then you have a disaster waiting to happen - the TGV will derail, the Président de la République Française will resign, the Government will fall, the Guilotine will be taken out of storage and sharpened - and it will all be your fault.