Outdoor enclosure for 48-volt Lithium battery

Hi All
After 43 years, I have decided to upgrade my power system.
I am switching from a 12-volt system to a 48-volt system.
My new Battery is a Discover Helios 48-volt lithium battery.
It has 16,000 watts and a 314-amp-hour capacity; it supports 10K continuous use and comes in a large, weatherproof enclosure that can be installed outdoors.
A built-in internal heater can keep the battery at the correct operating temperature.
This battery works from- 13°F to 131°F, but below 47F the internal heater would run.
In a warm climate, this would not be an issue. In northern Montana, it would be a big deal; I'd use power just to keep my battery warm overnight when I'm not even using it.  During a typical winter day, we never get near 47F. This means the battery heater would be running 24-7... not acceptable.
Although considered completely safe for an indoor installation, with double internal shut-down switches in case of thermal runaway, I cannot bring myself to install this inside our old cabin.
So, I have constructed a fire retardent brick vault, insulated, cement-lined, attached to the outside of the cabin.
Two 1.25" holes for the large power cables and two three-inch holes are drilled through the cedar logs to allow air to circulate from the cabin. Shorty core is only 6-7 feet from the wall; warm air is not lacking.
I will have a temperature probe inside the box to monitor temperatures, and if needed, I can use a muffin fan to force warm air through the box.
I still need to put metal on the roof, but for now the new battery room is ready for the 300# battery to be moved in.

You don't mention anything about the solar resources used to charge this system.  That is going to be very important.  What's going to happen when winter storms blow in and you can't get sufficient charge for weeks at a time?  Will there be a backup generator?  I could envision your batteries being totally drained by day 7 of an extended storm?  Will there be periods of time you are away from the cabin, or will you be there 24/7 to tend to the system?

For my own 48V system,I started with 4500W of panels, in five arrays, all facing South.  I later upgraded the system with another 3000W facing due West to catch the late afternoon sun.  This was done to prolong the time I could keep my well-pump, and air-conditioner running in the late afternoon without any battery depletion.  The South-facing arrays start getting shading around 4:30pm or so, and are all in complete shade after 5:00pm.  With the Western arrays, I can keep the well-pump running till 6:00pm, and the air-con running till ~7:00pm, before the battery starts draining.

What's the reasoning for keeping the battery outside?  Is it the potential for a run-away battery fire?  If that's the concern, why build the enclosure right up against the wooden wall of the cabin, made with especially flammable materials?  If in fact the battery were to catch on fire, the outside wall would light after just a minute or two, and then work it's way up to the roof.

Since my battery bank is in an unheated North-facing utility room, I went with lead-acid Rolls-Surrette batteries.  After 5 years, they are still performing like new, with all twelve 4V batteries reaching full charge by the end of the day, even in the rain.  On a sunny day, ~ 10:00am.  The key for keeping lead-acid happy is abundant charging.  The legacy of the many, many, many dead off-grid systems comes from the chronic undercharging resulting from implementing too few watts of panel charging.

Hey Mike;
There are 4100 watts of new panels waiting on a pallet.
I will post all about them when I get them installed.
Same with the Victron inverter, charge controllers, and the Nucleo smartbox.
My entire original 12-volt system must be removed first.
I'm old, retired, and working alone; things happen when they happen.

The battery is outside for several reasons.
But fire is indeed one of them. I had a friend lose an entire house and several pets to a lithium battery fire.
As for my outdoor fire-retardant box:
Compared to having that battery in the living room, it would first have to burn through the metal box, then burn through the cement board liner.
After that, it sure could catch the wall and roof and burn the house.
However, the time frame might be a bit longer than 2-3 minutes, and my freezeless hydrant with 125 psi gravity water is 25' away from that box.