This storage period and temperature are fine, although that is REALLY friggin' cold. At this storage length, you'll want the batteries to be around 50% State of Charge. The self discharge of these (or any) lithium ion batteries is not significant over this period, so you don't need to worry about the batteries draining themselves down to nothing as this would take years. You do, however, need to worry about storing at full charge levels as this can reduce the overall capacity "retention" (new batt term alert!) of the battery pack at the end of the storage cycle.