5Ky, you where asking about the screen technology for the GPS. It's what we call a transflective display, meaning that it is build to be sun readable and can also be used with a backlight.
It's the same sort of screen that Pebble use for the Time, and garmin for their own smartwatch and some other outdoor based GPS.
The main idea is of course as outside there is generally plenty of luminosity (direct sun or not) we can read the screen without the need of a power hungry backlight, but we still keep a backlight in case you want to use the device at night or indoor with poor lighting. So your 17hr test is even wrong because no one would use this specific device with a constant backlight on, I'm sure that without the backlight we could gain, at least, from 2 to 5 more hours of run time.
For the screen there are plenty different type of transflective screen, some of them are coloured with and without a backlight (like the Pebble Time and it seems this garmin GPS) some other are coloured with the backlight, and grayscaled without (like the PixelQi screen)