This looks like an interesting option for older Leafs: https://fenix.systems/news/fenix-news/2018/09/25/press-release-announcing-c5-leaf-pack-and-baas-products From a facebook post, John Bysigner claimed that "Yes there will be thermal management, the charging experience will be identical to the stock pack. As for capacity we can deliver 30kWh with our design, but need to validate compatibility with 24kWh cars. At a minimum you can expect identical capacity to stock." If an older Leaf could get a 30kWh pack with thermal management, that would be a huge improvement! And while he claimed that the "charging experience will be identical", if it has thermal management it seems likely that multiple quick charges on a road trip might all be able to get close to 50kW. On the other hand, you are stuck paying a monthly fee for the battery, which sounds like it's in the $100-$200/month range.