Power consumption

I am using a 7" tablet on a motorbike as "moving map". Because MFN shows almost no roads when beeing in overview-zoom-level I am using Osmand for map viewing (plus AFTrack for nmea-logging). Battery level in this case decreases about 10 % per hour with the device connected to board power (that's bad enough but I dindn't find a way to feed the tablet with more power). Short time ago hvdwolf mentioned something about "more roads visible in map mode" and therefore I decided to give it a new try. Besides the fact that i didn't see more roads than before I noticed that the battery level decreased about 18 % per hour, only displaying the map and logging nmea, without navigating. This means that after about 5 and a half hour the tablet went down and I had to switch to paper mode.
Has anyone of you compared power consumption of MFN vs. some other navigation software?

p.s.: When using a normal phone navigating with MFN the device stays on 100 %, so here it is no problem.