My experience of last 6 Month says,
If I travel on highway 100-120 km I get 21/22 km/hour.
If I travel local 60-70 km, I get best average 23/24/hour.
If I travel in rushy areas, 20-30 or max 40. I get worst average. 14/15/16.
So I think it depends upon how you place your feet on accelerator and how much speed you maintain during travel.
If you are not getting same kind of results, you should get your Battery cooling system serviced. That may change results for you. Its summer start, May be I will also do same just to make sure, batteries are good.