I don't think we'd need that many batteries. Something like the WAW needs ~1k watts at 55mph, so if we increase the weight by a factor of ~2, then it'll need ~1100watts@50mph and weight ~700lbs since the 10N difference in rolling friction is small compared to the ~55N required to overcome fluid friction, so an extra ~350lbs only increase the power required at 21.5m/s by ~15%. A L16H will provide 75 amps for 3.75 hours, and three of them, 225 amps, which is 1.35kw at the battery, enough to go ~50mph for ~3 hours assuming we drop to 80% DOD, so ~150 miles.
The advantage being the battery pack will only cost ~$1k and will go over 100k miles, compared to anything else which will require load balancing, cost more, and may not loast as many cycles. The cost being ~1 cent per mile, maybe less as time goes by depending on if the rider doesn't mind having less and less range over time past the 700 cycles. If they can stand the range dropping down to 50-75 miles, the pack may last ~150k miles. Costs would drop even more with the cores on the used batts.
If we're going for high performance, going with NiMH or Li-poly/ion would be the best bet, but they are more expensive per kwh, won't run as many 80% DOD cycles, and are relatively fragile. We can also reduce the reference area, but this impacts the cargo space and relatively large size of the vehicle. Provided the motor/controller last as long as they are rumored to, this setup (extreme economy so to speak) should be half the cost of a gasoline setup during the same timeframe.
I've seen a NiMH that comes close to the lead acidsetup, >1000 cycles at 80% DOD, .1C rates. But it requires the rider to average ~25mph, or else get a really big pack since going ~25mph at .1C rates requires ~200-300 of these 1.2wh batts. A nice advantage is being able to pull 300W from each, for a total of 7.5kw of peak power, much more than a comparable gasoline setup (a gx25 I suppose). But, neway, if the same pack is taken to 50mph, the number of cycles drops down to the 400-500 range, so they cost twice as much as the deep cycle sla. What's really nice about batteries is they can be scaled w/o the loss of efficiency associated with the different sizes of gasoline engines available.
edit- i don't even use proper units when i'm not making mistakes.