Some cells will reverse polarity or experience other damage when cell voltage gets too low. My earlier point is people have an ignition designed and intended to be run on minimum specified voltages. It may be 4.8v, 6v, or 7.2v. Doesn't matter. Why, and I'll repeat that, why, would anyone have a need to run their ignitions at voltages less that specified by the manufacturer? Are modelers today really that stupid?

If you are running a 4.8v ignition with a 4.8v battery, where is the logic in using the battery below 4.8v? In any case, the engine will tell you when the battery is too low. Hopefully you have enough time to land safely before the engine stops. If you check your batteries, and I hope you do, it should be able to hold a 1 amp load and maintain 4.8v if it's a 4.8v battery. For flight batteries it better be able to hold a 2 amp load.

Speaking of Eneloops. I put my Yak away around the end of September last year with a fully charged 4.8v Eneloop on the igniton battery. Pulled the plane out yesterday and checked batteries for the first time this year. The Eneloop was at 5.2v. Not shabby at all for a nimh.