In addition to the furnace blower, the refrigerator controls and LP gas detector will draw power too. Depending on how cold it is and the type/condition of your battery, your battery won't last very long. With a typical single group 24 battery in healthy condition and not very old, you'll probably find it'll last about a day with temps in the 40s-60s. Maybe less depending on how much the CPAP uses.
Do you have a generator or some way to recharge the battery?
There are some other battery options that can extend your range, but unless you want to go off grid regularly, it probably doesn't make financial sense.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR