Two 2700 mah NIMH batteries in parallel should produce 5.4 amp-hours of capacity. Given that a glow plug typically pull about 3 amps and there are two plugs, the draw should be about 6 amps total. 5.4 amps capacity / 6 amps load yields a "run time" of 0.9 hours, or about 54 minutes. The glow driver should be wired through a micro switch on the throttle servo so as to only turn on at low throttle (idle) so it is only "on" during engine start and at idle to keep it from flaming out. So, unless you spend all your time taxing, this set-up should work just fine. If it is wired to run continuously, then a larger battery would be needed if you intend to fly for more than about 45 minutes per flying session.