Absolutely right. With a 48 T chain ring cruising at around 27, 28 on high destroys the battery in no time but its hugely dependant on the wind direction. You probably wouldn't even get 20 miles out of it into a headwind. In such conditions I've found it better to ride in 9th, put it in standard mode, and cycle with a much faster cadence, and cruise around 25. I'm probably doing a fair bit more of the work but the range is hugely improved despite being only a couple of mph slower (I've ridden 27 miles into a 12mph headwind like this).if you ride a steep climb non stop then its going to pull the same power just cut out after 15mph.
also it did go as high as 18 amps
remember with a dongle you can use a lower power setting and not have it cut out it still will use a bit more batt but not that much.
the tipping point for me anyway is over 25mph then it nukes the batt if you keep hammering it at those speeds.
you will still get around 20ish miles out of it tho.