mrasmm

looks like choppers beat me to it =P

you can run the motors singly, or you can run them in parallel, or you can run them in series. For the motors I've done, I find that somewhere around 1/4th to 1/3rd of the rated voltage you will run them works well for seating the brushes, while not over heating the motors. Even without a load on them many of these motors get quite hot because the windings are basically a pure resistance load. To do that the best option for you would be to run the motors in series. Which is one lead from the battery to one pole on the motor, connecting one pole of each motor together, and connecting the remaining pole to the other lead of the battery.

Of course the polarity of the motors during break in can make enough of a difference that I think it's worth checking, like choppers already suggested.

Also with your pack since it is rechargeable the LVC (low voltage cut off) is going to be a big deal for the life of your pack. 1.0v/cell under load for NiCD and MiMH, and 3.0v/cell under load with lithium packs except a123's, and with those LVC truly is not that big of a deal. If you are just hardwiring to a pack, this could be very easy to let slip by, and it could damage or reduce the capacity of your pack, especially in the case of lithium packs. If you have something like an exquinox (or the hyperion or a bunch of others that are the same thing), it will work great for this purpose with lipo's.. Set it to the same mode you charge in and use those leads to hook to the motors. It will only allow it to go to 3.0v per cell if I remember right (it's either that or 2.7v per cell, which is a little low), and then it will shut off.

Good luck =)