My riding has gotten a bit more aggressive lately; before i was doing like 20-25mph now im at like 27-31mph so that changes the average mpg a bit. The break even point where the gas generator provides most of the energy for a light rider is 20mph so 17-20mph or 420W (note I only use 50% of generator power for engine health).
At this level, the mpg is like 150-200. At my current 27-31mph, I use about 1V for 4 miles which gives me a range of 45-50 miles of hard riding (82V to 70V resting). I am not sure what the mpg calculates out here as what exactly is MPG defined as in this point???. But, at these speeds, I will need to stop and let it charge up. But, if you slow down to ~20 mph you can go like 100 miles (82V to 70V).
The only issue I have had with the generator is that the pull cord rod retract apparatus got worn a bit so it would not catch on the flywheel step; I simply cut off about .200 from the plastic casing which moved the worn pull cord rod .200 closer and its all good now. That's it.
So, the generator I got on sale for $150 and then like $20 in mounting materials. This is $170 to get the same performance from batteries would be like $400-500. Both are as reliable imo. But those batteries would be like 4-5x as heavy but also no noise.
That being said, I think this is definitely a viable option with amazing stealth flexibility and reliability. I think a budget build would be 1kW hub, 48V 12-15aH battery, 800W generator, 420W charger/constant power source. This would be like $150+$250+$150+$50 = $600 without the bike or materials (since many of you have these already). With the hub motor, you should have literally no issues with the setup short or long term. Of course, this is like 3-4x the cost of a good 2 stroke kit and 2-3x of a 4-stroke kit. Probably ideal for those already with an DIY electric bike looking for more range and flexibility. But, I dunno a fresh build might be worth it in terms of stealth and reliability. You will need a cruiser frame to do this though; no way you fit this in a mountain bike unless its the straight top tube with big inframe triangle (mebe).
Of course, I am thinking of playing full electric next build with legit self made motorcycle registration (6kW motor + 3kWh of LTO batteries + onboard supercharger). This bike should do 60mph so close to a 125cc bike and LTO is like 10k cycles and high discharge/charge. Even if I do this, no way I will break down the current hybrid; I really like it and its a great convo/proof out piece.