I know batteries to generally be safe but am wondering if any folks are putting the battery systems outside of their home, let's say in a shed, detached garage, or a purpose built enclosure for batteries?

We have ours in a porch - mostly because the fan is slightly noisy.

I think the main consideration for any outbuilding would be whether it was water-tight, had some level of climate control, and was secure against theft.

Thanks, I think I saw some reference somewhere to consider the lithium in the batteries and safely keeping them in any space.

This would remain relative to climate and security needs though as you're pointing out.

In a cold climate you have to add heating and an insulated enclosure to keep them alive.

Bury them below the frost line in a concrete box with a sealed access port, add in some water cooling for when the battery heat goes above a cutoff. They'd never get too cold that way, stay around 60 Fahrenheit by default.