Left seat heater cushion plugged in overnight- no power to lights and starter. Tried jumping but no power then either. Could some fuse(s) have blown?

 

did the battery freeze?
if yes, its probably nfg and a bad cell will suck all the life out of a booster battery or booster vehicle. have the battery tested, if its good have it thawed and fully charged. if bad replace.
....the answer to the next question is....in the floor by the passenger middle seat