My experience with the booster batteries tells me that the ideal replacement for our pack would be a lithium based pack with the same max voltage as our pack (~177v). With MIMA to increase the electric use, and a 20-40AH useable capacity, we would have a +100MPG car with a 2-3 hour boosted range @ 65-70 MPH. Drop the speed to 35-45, and we could be looking at 3-4 hours of +100MPG electric priority. Of course the pack should have grid/solar charge capabilities.
Only time and money are needed to make it happen.