ML320 CDI battery change question

[loggo]

Just a quick enquiry. I am going to have to change the battery on my ml 320 CDI 2006 vintage as a cell has gone. It seems to operate pretty well at 11.9 V but I can't confess that im very happy. My question is do I need to arrange for an alternative 12 volt power source whilst I remove the battery to protect various electrical gubbins or can I go 5 minutes without power and suffer no Ill effects like we used to do in the old days !