Question about Medela Cooler bag with 4 milk bottles and 1 cooling element

Put it in the freezer at -18 degrees for a few hours until it is completely frozen.
Alternatively: It's no problem if you need to move quickly, the bag insulates quite well, so that even a not completely frozen battery or a smaller one can easily be transported for 2-3 hours. For example, we often froze the milk... :)

I always put it in the freezer for one night and pre-chilled....