Just to add to the mix - I recently installed the Maxamps 5500 mAh saddle pack into my BJ4. Modifications were as simple as trimming the battery tray to wedge the pack towards the center of the buggy (I can post some pics if anyone wants to see them). The saddle packs are taller but I used a longer 4-40 screw to engage into the post with no problems so far. The pack sits directly on the chassis now.
I am running at GTB/5.5R (bulky) so when I checked the weight after the battery change I was just above the ROAR minimum. On the track the buggy handles great so I don't plan on adding any weight. I had someone try my buggy the other day and the first comment they made was that the buggy ran nice and light
Hope this helps. Brushless and Lipo's are the way to go - very, very, very low maintainance .................. more time to practice
