Are the packs warm to touch??? when charged???

Charge leads will charge NIMH, its pulse chargers that shouldn't be used on them.

Do you run the car until the car no longer moves?, or do you stop when you notice a drop off in power?

To be sure take the Charger, and batts on to the shop where you bought the stuff from and ask them to take the stuff for a day and see if they can get both packs to charge properly...

If they say know well then you have a problem.