What chemistry do the replacement cells use?
The LEV50 is old chemistry, I believe it's LMO (Lithium Manganese Oxide). It's hard to get those cells any more. Most modern cells are NMC (Lithium Nickel Manganese Cobalt Oxide). The curves are different enough that the iMiEV's BMS will think that new cells are terrible, and will give a low estimated range remaining, and this estimate will get worse with time.
I've tried current spoofing, with initial success, but eventually it gets really unreliable. This was on a vehicle I don't own, I was just celled in to try to help. There is not enough data to know what's going on as yet.
Others have also reported difficulty with just replacing the cells, unless LEV-50 or LEV-50N cells are used.
Edit: the LG E63s are definitely not a suitable chemistry, unless you do something drastic like replacing all the CMUs (Cell Management Units), generating all the CAN messages that the BMU (Battery Management Unit) needs. Or replacing the BMU as well, generating and handling all the CAN messages between the BMU and the other computers.