Svar från Garmin
Här är svaret som jag fick från garmin.
"Power-save mode works by detecting if you are following a steady
course/speed, if you are then the receiver switches off for a few
seconds. The screen is updated as normal, based on this course and
speed.
When the receiver switches back on the run-up position (a DR or Dead
Reckoned position) is compared to the actual position, if they match the
receiver switches off again, if they don't the receiver stays on until a
'steady state' is detected again.
The battery save mode is not really recommended for slow moving
applications like walking, due to the slow speeds."