is it in full maxx mode that they switch to the lower setting.
i have the maxx-d & have no issues even in cold weather.
one thing to note is that the yellow 50% light will come on in either of the low settings if there is only 50% left in them paticular modes but i can then knock it up to maxx mode & the fuel guage shows green.
the fuel guage works on the principal that if im in maxx mode roughly quoted as 3 hours it will remian green untill 505 of the battery in maxx mode is used but if in then switch to a lower setting it may turn the fuel guage yellow even though i am using less power it has calculated that i may intend to run the light for up 10/24 hrs respectivly.
hope ive explained it ok .
also worth noteing that to get an optimum charge it is best to leave the light still connected to the charger for a few hours even when the light on the charger turns green this tops up the final 10% of the battery.