That will work just fine. I've had good success with Hydrimax receiver packs. Recently I've been buying A-cell packs from http://www.cheapbatterypacks.com, they are usually cheaper than the Hydrimax packs, and work quite well.

The higher capacity packs will weigh more than the stock 4-cell packs, so be sure to recheck your balance after swapping them out. In most cases you probably won't have to rebalance, though.