quite a few times i've come across the very same problem the OP is pondering about
and yes, an average 20 lbs bike can turn into a 36 lbs brick easily once the battery juice is out
and you are stuck pedalling at like 6 to 9 mph, which is a major drag if you a long way from home, or the nearest power plug
sometimes it feels almost faster pushing/running the bike than trying to ride it when the battery is out
for that very same reason, i'm now in the process of researching battery extensions, and other alternatives to recharge the battery while riding
regardless of what people says, the
regen power thing,
does not work in real life situations, unless you have a very very long hill to ride down slowly like at 10 mph so you can take a good charge
but no sane mind will waste a good hill to go down at top speed, so you don't have to pedal as much on the up hill on the other end of the valley
what comes down, must go back up
the regen energy works great in a lab, or if you don't mind being a slow poke riding at the slowest speed to recharge your battery, which I've tried it does work, but it takes a painful 10 miles to only get barely a 6 min boost or 1~2 bars that will go away in a swift as you hit the throttle