Interesting video of a battery upgrade of a 30kWh Leaf Taxi which has done about 94k miles:
Rather than just replacing the old battery completely for one that is more dense and higher capacity (expensive!) the Muxsan upgrade kits take the approach of essentially adding another battery in parallel with the original, mounted in the boot with a new higher false boot floor.
The description of the video says the original battery is degraded but I've actually posted a query about that in the comments because at one point in the video before the additional cells are connected they show a claimed range of 90 miles from 86% SoC - which is actually pretty normal for a 30kWh Leaf in November! So if it is degraded it's not by much.
Full charge range after adding the additional battery is 168 miles vs around 100 miles for the original car like mine, and a heck of a lot cheaper than replacing the entire battery, the downside is it took them nearly 2 days to do the job (their first time though, they reckon they could do it in a day now with the experience they have now) and you lose about half of the boot capacity, but the Leaf boot is pretty big to start with.
Probably not what you'd want to do for a personal car but for a Taxi adding an extra 68 miles of range to an existing car that's already paid for itself with low running costs over 94k miles seems like a reasonable thing to do vs buying a newer car.
I noticed as well that when they had the main battery pack out the under pan of the car was absolutely spotless and rust free, fingers crossed mine is the same!