Are you guys using the Tech Aero Ignition Battery Eliminator? This device allows using a common battery for radio and ignition.

I use an 1800ma LiPo in my pattern gas set-ups, powering radio and CDI through the Tech Aero unit. I stop at 75 minutes of flying per charge....voltage reads 7.4 to 7.5 volts after flying, which is nominal voltage for a 2 cell LiPo.

My gas set-up is 2 stroke; so the 4 stroke must be realy banging the control surfaces around....interesting!