The best way I know how to test it is keep rpms low, and give it lots of throttle. This will use assist and drain down the pack. Other owners who have had their cars for more than 2 days can probably provide more info.
As for fixing it, the general consensus is its best to try to rehab the original pack than spend on replacing it. There is are designs online for a charger/discharger that allows you to cycle the pack and this generally improves the battery condition. Its not a sure fire fix, but it generally works to improve battery capacity and it will help balance the cells.