The colder the temperatures get, the shorter it will last.
Bear in mind, that allowing a battery to discharge to 50%, or less, is not advisable.
I have my spare battery on constant trickle charge with a smart charger and it is therefore always available, albeit at home, so it remains 'available' at all times.
I have hefty jump leads in the van.
I did consider one of those instant starter battery packs, but never got around to buying one.
It is essential for all members to maintain their starter battery in good condition and fully charged throughout the winter months.
Of course, if you use a spare battery, you should ensure you recharge it fully asap.
I have also noticed that if I do not maintain my spare battery on trickle charge it can take days to reach full charge in cold weather.