It seems like adding more battery to a Leaf could make sense financially. Even if you put this on a trailer, $300 for the trailer, another $100 for the plywood, around $3,000 to $4,000 in Jehu Garcia approved 18650's for another 24-30kWh. $1,200 for a separate BMS and at least another $1,000 for cables, bus bars, connectors, contactors and Arduinos. So at around $6,600 you could have some what close to double the range, as long as you don't burn anything down or get electrocuted in the process.
That beats owning a second vehicle. Well, the total cost of ownership of an average, cheap, used vehicle for 5 years is between $25,000 and $35,000 in the USA. Edmunds TCO calculator guesstimated that my Leaf would cost me $21,000 total cost of ownership for 5 years. Adding a $6,600 battery trailer to a used Leaf wouldn't be as cheap as owning a Ford Fiesta or Mazda2 as an only vehicle, but it would be close. And it would definitely be cheaper than owning a second car.
Of course the more sensible thing to do is patiently wait until Tesla 3's, Chevy Bolts and Gen 2 Leafs can be bought as cheap used cars.
2013 SL SOLD
1972 VW Beetle SOLD
1984 VW Golf diesel CURRENT
2013 Toyota Avalon Hybrid CONTEMPLATING