[folivier]

The compartment my batteries are in are just rearward of the water bay. So they get some residual heat from the aqua hot. This past winter it stayed within a few degrees difference after I lined the compartment with a layer of that foil faced bubble wrap insulation that Lowes sells. Never got below 45 F. There is also an a/c ductwork in the ceiling of the battery compartment so it receives a bit of cooling as well.
Thinking about it it would be easy to loop a piece of the aqua hot water tubing into the compartment for more heating if needed.
Good to see a company pushing this technology. It can be a game changer.