Yeah, I have total range paranoia on my longer rides because they have so much vertical, which means that so much is dependent on intangibles-- how much energy I am adding to the equation, wind, heat, etc. My longest ride so far has been about 32 miles with just over 4,000 miles of vertical, and I had about eight miles in reserve.
There's about five or six more miles of flat terrain I want to explore at the top of the highest ridge-- and when I was up there before, I could manage the sections I did ride either without motor or in "Eco," with only the occasional blast of "Norm," meaning low battery usage. But I think for that ride, I'm going to have a bug-out plan-- if I run out of juice, I'll have my wife to a local breweryon the way back that I know I can make it to-- and have her bring my charger and an extension cord. My house is at the top of a long-ass hill. I'm not doing that unpowered, particularly after a ride like that!
Not after riding the bike for a bit, and realizing the power required to maintain speeds over about 15 mph will suck a battery charge at a pretty good clip....
Depends how hard you are working and what bike you are riding. For me, I recently discovered that I can manage a pretty high cruising speed on fitness rides with flat terrain. Yesterday, I got 9.1 miles out of the first of five "bars" on the battery indicator, while usually, I get around 7 to 8 miles per bar (with about 1,000 feet of vertical). This included a lap around the Griffith Park Reservoir-- a little over 3.5 miles-- which I took in Eco, working hard. The E5000 is so underpowered, and the bike is light enough that the drain on the battery is low and steady even close to the Class 1 assist limit. The indicator shows the system is only delivering 10-15% of the available power, but it's enough to help me get that 46-pound bike up to pretty high cruising speed.
Speed only dropped below 16 MPH to get through gates and for one rolling stop (to check in w/ the rangers, it was 5 minutes before the trail closed, they took pity on me, opened the gate, and let me take the last segment! Got to the last gate 30 seconds before closing.) Top speed was 19.2 MPH, did over 3.5 miles in about 13 minutes. Drenched in sweat when I got back, but it's a blast cornering at those speeds-- the curves are tight enough to be interesting, but not so tight that I'm pushing maximum lean (which would mean pedal strikes.)
There are definite drawbacks to having a lighter, underpowered bike, but there are some advantages, too.