I don't currently have an ebike system, but I'm toying with the idea of designing a hybrid bicycle and playing around with it. Is there a system on the market with a 100W motor and weighs ~5 lbs including batteries? I figure 100W is roughly half of the power I am putting into the pedals at 20mph. The battery would be sized like a hybrid car battery, IOW, it'd provide a boost on acceleration and hills, and drag slightly on the flats and especially downhills to charge the battery, so the battery pack would be significantly smaller than the normal (from what I can see) ebike system.
The way I figure, it'd be plugable, but it could also work as a closed system that never requires charging, like a hybrid car. Is there a system like that on the market or in someone's garage?