It will not charge with the stock charger. Charger will need to be modified to charge 2 cells. If you are using a modified charger and still have this problem, you may have a bad cell.
I have done the motorworks steering in a zip zap. Two steering springs help. I had the best results using all the zip zap steering components, except magnet and coils. Make sure the magnets sit flat against the sides of the chassis, trim with exacto knife if it won't fit. I wound my own coil for the steering linkage, I could not get the one out of the motorworks linkage (glued in too well).
Here is a link to coil making. I have tried other methods, this is by far the best (easiest). I used the coil out of an old motor starter as the source for my wire. It is just a bit larger than the stock wire (less chance of breaking it later). I made the coil in my 11 mph pro stock dragster using this method, but I made it real wide so there is very little steering (coil hits magnets).
http://www.geocities.com/pfabersac/coil.html