CeeGee,
You do not have to run a regulator with 5 cells, you just get more torque and speed with a minimial weight addition vs 4 cells. These are the best they use Sanyo cells:
http://www.cermark.com/Merchant2/mer..._Code=5HR-AAAU weight is 2.5oz. Here is a cheaper solution I use these on my combat planes and have never had a problem.
http://www.balsapr.com/catalog/battN...ductId=T658584
weight 2.3oz
Hope this helps