To answer the OP's question, the difference is due to the smaller battery in the Harvester. Why is this so? Li-ion batteries (all batteries actually) have a maximum safe discharge rate. This means that the total amperage available is a function of the battery chemistry and the number of cells (and to a lesser amount, how they are connected, serial vs parallel). So assuming 2 battery packs with the same chemistry and pack voltage, the larger pack will be able to provide more amperage at the same time(cell-level) discharge rate.I just saw the following regarding the 0-60 acceleration:
Scout Motors projects that the fully-electric versions of the Traveler™ SUV and Terra™ truck will accelerate from 0-60 mph as quickly as 3.5 seconds.
Scout® vehicles equipped with the Harvester™ range extender are anticipated to accelerate from 0-60 mph as quickly as 4.5 seconds.
I did ask chat why the difference and the Harvester is coming with a smaller battery. This wasn't conveyed when I put my reservation down for the Harvester version and I must be honest that I'm very disappointed in the reduced performance. It would be nice to have the option for the performance along with the range extender.
It's good that Scout is being upfront about the difference. Tesla got into hot water (and actually lost a lawsuit) where they advertised the combined horsepower of the motors but due to the pack size and chemistry, it could never supply enough power to hit those numbers.
As Thomas Sowell said, "There are no solutions, only trade offs." Bottom line is that the only way to increase performance is to increase pack size (until the pack can supply the maximum power that the motors can use, at which point the motors become the limiting factor). I am sure that Scout is carefully considering the balance between weight and performance on both BEV and EREV models. We should have all of the information necessary to make a decision prior to creating an actual order and committing to purchase.