The outdoor temps are sub zero all day long at the moment. It's not easy for me to take the battery off the bike when I get to work and it stands all day outside, so even though the bike is stored in the warm over night and recharged above freezing, the trip home is with a sub zero battery. Has anyone got any info on how damaging this is for the battery? Is there a temp you must not go below for safe use of lithium batteries (not including charging - which must be done above zero).