If battery technology can continue evolving, I think we'll see a number of electric sport planes for the weekend pilots in 20 years. I don't see electric replacing fossil fuels for long distance transport though. First of all, it would require a large investment in charging apparatus at all airports, and I imagine every different make will have a slightly different charging plug and amperage requirements. You can't expect Cessna/Piper/Cirrus/Diamond/etc to all agree to one standard now, can you? 100LL will go away, (I hope) not because I think my 172 has a measurable effect on the environment, but because the lead fouls my plugs anyway. I'd love to put a good un-leaded auto fuel in it, but the Govt feels compelled to bastardize it with corn alcohol, which also causes my horribly inefficient lawn equipment to suffer.
How about a zero-turn 48" cut electric riding mower for $2000?