We live in the mountains of Idaho and expect snow staring this Week. Is it safe to store our new bikes in the barn or do I need to keep them from freezing?
If you read the instructions that may have come with the bike, it will give you the operating and storage conditions. They are probably +40dgC to -5degC. I can't recall accurately, but for sure I would not like my battery to go below freezing. So, if you believe that your barn may drop below freezing, just remove the battery and keep it anywhere in the house free from freezing. Charge the battery to 60-80% for the storage period.
If your bike has a battery that is not designed to be removed, then I would rather keep the bike in the house somewhere out of the way than risk a below freezing period. But still charge the battery to 60-80% for the storage period.
PS: You may be surprised to know that many emtb riders in Scandinavia ride through most of the winter. Hardy souls, but they have learned how to look after their bike in well below subzero temperatures.