Unfortunately, most battery gauges are not very accurate, this is basically because they measure the battery's voltage rather than the battery's consumption (The total current that the battery has actually delivered throughout the ride).
The accuracy of the Smart Display will also be affected by the chemistry and the number of cells in series within the battery.
LiFePO4 and LiMn experience different voltage drop throughout the discharge of the battery, and there is no provision to adjust the battery type/voltage between a 12S or 13S LiMn, or a 16S LiFePO4 battery pack, all of which are all often described as 48V packs.
Realistically, a 12S LiMn pack has a nominal voltage of ~44.4V, a 13S LiMn pack has a nominal voltage of ~48.1V, and a 16S LiFePO4 pack has a nominal voltage of ~52.8V, so there can be a big variation in the actual battery voltage.
Basically, if a battery gauge does not have the ability to set the exact battery type (the number of cells in series and the cell chemistry) then it is unlikely to be very accurate.
Alan