I have seen the triangle appear just as the regen limit due to cold weather is going away. Typically, the energy graph looks like lymex2017's picture above, with just the dashed lines on the bottom (and sometimes top) of the energy display. As the battery warms up, the lines go away, and then just around when they disappear I have seen the triangle. It comes and goes though, so I can't say for sure what triggers it.