Motorists have been warned they could start 2017 on "a flat note" if they leave their cars idle for too long.
The RAC attended nearly 10,000 breakdowns on the first working day of 2016 - up 40% on a typical day - with a third of cases attributed to flat batteries.
The firm recommended that cars not used over the Christmas period should be driven before they are needed to get to work.
It advised motorists that a 30-minute drive could be enough to top up a flat but otherwise healthy battery, reducing the chances of a breakdown at home.
RAC spokesman Rod Dennis said: "Traditionally, the first day back at work after the Christmas and New Year break is one of our busiest for breakdowns.
"With millions of multi-car families in the UK, the long festive break often means at least one vehicle is not driven. Each of these unused cars represents a breakdown waiting to happen.
"Not running a car for a long period dramatically increases the chances of a flat battery so motorists risk starting January on a very flat note.
"Our advice to motorists is to give every car in the household a good run before the new working week.
"That way they can be much more confident of getting the new year off to a good start, rather than off to a non-start, and lessen the chances of having to ring the boss and explain why they are going to be late for the first working day of 2017."