[bovva66]

Just had similar problem, turned key with little effect after Sat night at friends for dinner. There was a brief power up, then everything went blank. Got RAC out, no luck getting it going, even with new battery. Had to get it towed on Monday morn to my local dealer....after a 4 hour wait for tow truck and issues unlocking gear lever (there is a manual unlock near footwell) finally got it to dealer.
Apparently when battery goes flat the system generates a large number of error messages, which have to cleared from system, before new battery can be connected. This was going to take a number of hours to correct, so had to leave with dealer and pick up next day. All up about $360, including $260 for new battery. According to dealer there is no way to determine when battery is going to die, so he suggested replacing battery every 3 years, as it was obvious to me the Mondeo does not like a sudden loss of power, and I don't want to be without a car for 2 days again, just because of a flat battery.

As I bought used MA 2007 in 2009, had no idea how long battery was in car, but assume was original, so about 3.5 to 4 years of life before battery was dead.