After little tinkering in battery specs, seems that it’s easy just to set warning trigger to 2.7V and emergency alert to 2.6V, when working conditions are above 0C. As voltage stays nicely at around 2.8V at 0-3mA currents.
If working temperature is little below 0C, constant voltage even on full battery is below 2.7V and start discharging very fast after 2.6V. So warning trigger is hard to set, instead we could set emergency alert to 2.65V just for sure.
For much colder temperatures like -20C, we have to measure battery’s behavior. As I didn’t find any test’s in freezing conditions.