Not as light as a butterfly, but the MeOH Power Cell generates over 1-watt-hour per gram
[lithium ion batteries are around 7 grams per watt-hour]
Methanol (MeOH) is the perfect fuel derived from oil, natural gas, CO2, any biomaterial
Safe as rubbing alcohol, just don’t drink it.
Inexpensive, easily obtainable and easily out-fittable for gas stations