Hi Gary,
Added weight for an ES is seriously little. FWIW, I've had the parts in my hands: preamp is a small circuit board with the 3 plastic knobs that weigh nearly nuttin, battery box is plastic where the battery itself is likely similar in weight, the body sensor/harness is mere wire. The only thing I haven't had my hands on is the fingerboard pup, which is a small, shallow pup which can't be much either. Moreover, I once had two GAs together, one with and w/o ES, and if I held one in each hand I couldn't tell you which was which. ES2 is minus the fingerboard pup and body sensor so that's even lighter. Hope that helps you
Edward