Hello,
I’m sorry to hear about the dead battery. We’ll look into how the battery has failed prematurely, thank you for reporting the issue.
CR2450HT is extended temperature range battery. Personally I’ve used a basic CR2450 from nearby hardware store (Clas Ohlson) both in freezer and sauna with no issues, however CR2450HT should have linger life in extreme conditions. CR2477 batteries work well also, and they have better capacity which leads to longer lifetime of the device.
-Otso