Lithium batteries do not self heat like lead acid, and even with lead acid it takes some significant currents which aren't going to happen at a solar repeater site. You will need to provide some heat which at a time of minimum solar insolation will be a hit to the power budget. The more insulated of an enclosure the less power it will need. Doesn't need to be 75F, just something north of freezing. As a data point, some batteries have their own thermal management which simplifies the design, just use an insulated box. Supplying the additional power will be the hard part.
Mark K5LXP
Albuquerque, NM