Your engine shouldn't use that much. I suspect your battery isn't very healthy, or it isn't getting a full charge. Why not try a new one. I'd go to a 2000 MAH instead of using two, but even that is a lot. On my 55cc, I have a 2000MAH LiPo and only charge it once in a whole week and week end of flying. On my Zenoahs, I use 1400 4.8 Nicads and fly all day.