Firefly specs the battery output up to as hot as 50C, but it does come with a caveat in their manual:
The optimum operating temperature for a lead-acid battery is 25°C (77°F). As a rule of thumb, every 8-10°C (14-18°F) rise in temperature will cut the battery life in half.
That's a pretty standard rule of thumb that any chemist would use for a chemical reaction, and I believe it is at least approximately true for all Lead-acid batteries.
Where Firefly might have a bit of an advantage is they have high charge efficiency, and very low internal resistance (specified as 4 milliohms) so they generate less internal heat during normal charge/discharge cycles. They MIGHT run a little bit cooler in the same ambient environment than other valve regulated batteries. On the other hand, a flooded cell that is generating gas will be losing a lot of heat that way, so I won't put money on it either way!
Fort Lauderdale, FL
Almost ready to be out sailing again!