A lot of times, when you bring a car to the dealer, and need to do anything to do with coding, they'll bring the whole car up-to-date computer module wise. This can involve several hours sometimes; not with a tech working on it the whole time, just the car going through the process by itself while hooked to the computer. Due to the potential drain on the car's battery, and the requirement to have a stable and proper voltage throughout the process, (to avoid screwing up any of your modules), the procedure is to hook the car to a power source. Some high end battery chargers have a setting to provide this stable voltage source, but you can also buy devices that only provide this stable voltage source (designed exactly for this purpose,) and don't charge batteries. Pretty much an essential for anyone coding or programming a modern BMW. Perhaps your tech did not do this, (being lazy and/or not expecting a long coding time,) and ran your car's battery down. And coding without this stable voltage can do all sorts of potentially permanent harm, especially if the battery is a little weak to begin with.

__________________
2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp