I have a Futaba 9Z trainsmitter. On a full charge of 11 volts I get 3 flights at 10 minetes each. My voltage goes to 9.7 to 9.9. I charge at this time. I would like to fly longer. Should I buy a 2300 nmh battery? Keep flying to a lower voltage? At what voltage should I stop before I take the plane into the air? Also you do not reccomend lithium ion battery packs. The mfg. say they have hundreds of them in radios with no problems. Why should we not use them? Thank You for this forum. Eric