No, it is not normal.
When driving with power connected, I find the battery stays fullish
(car, but surely your motorcycle can provide 500 mA at 5V!).
I have had problems when not only running osmand but also running an
opencellid tower collector and not being in cellphone range for an hour.
But it was mostly overheating, not battery running down.
When hiking, I find that using osmand (GPS and screen) for an hour
really does use a lot of batteery. Maybe not enough to go from 100% to
0% in 1.75 hours, but 3h wouldn't shock me.
I guess you should check to see that your phone really is getting power.
Also I would put the phone in airplane mode if you are riding where
there isn't cell service.