With a bench power supply (or a similar ghetto version, that is any lion charger plus leads) you can charge single cells even while they’re connected in series. That’s how battery balancing works
I’d start with very low amps and maybe low voltages too to revive them
Heat pump and dual direction charging are awesome though. I don’t imagine they’re using these kei cars between the cities when they can get high speed trains.
Nissan could easily take 5k off but has been hesitant/gradual with EV adoption just like the rest of the Japanese producers.