Uh, the problem isn't the bike, it's your mental process. If you really want exercise, then before you ride make a decision on when you will use assist and when you won't and stick to it. It's not good for the battery to completely drain it. Use a little willpower and you'll be fine. Just decide no motor on the way out, or no motor except on the big hill at level 1 or whatever. I'm sure you're partly joking, but it can be too easy to take the easy way out unless you decide not to. Get a cadence meter - if you ride at 70rpm without the motor and level 1 takes you up to 80 rpm, them decide to push to 90rpm when you use the motor. Instead of letting the motor make all the difference, up your speed and cadence proportionally with the motor. So you'll go faster with the same amount of effort you put in without the motor, but not using less effort.