Lithium battery container

[mihit]

Everyone's pretty well covered it, but I'll chuck my 2cents in.
I'd go a small concrete slab and brick/block bunding for a couple of courses, then light timber or steel frame. Can double-skin it with corrugate (cladding and lining) and fill wall with whatever insulation. expol, glass batts, foam, hemp, whatever.

The BMS should control charging temps, solar panels tend to over-volt in the cold.
...and if you do end up with thermal runaway then temps all become irrelevant reallly quick.

One thing I thought to.mention, you said you need to consider cable length etc, I figured from a cost perspective but also there is the voltage drop over distance, I'm sure an extra 20m won't have that much effect but might pay to get an elec to advise

There are plenty of tables/calculators available online to gauge cable for distance. And the cable supplier should have them on-hand.
48V is pretty copper-friendly, though it's always better to do the long cable runs at higher voltage, ie, put the inverter close to the battery and run 240VAC over the gap, if possible.

6kW @ 48VDC is 125A which would generally be serviced by 2x25-35mm cable and your resistance is going to be in the order of 0.5R/km, so negligible.
6kW @ 250VAC is 25A wich will be serviced by 2c+e 6mm TPS. which if anything like NZ, is going to cost about 1/10th the DC cable.

https://www.engineeringtoolbox.com/w...ges-d_419.html