Both Batteries were NMP's. They were never charged improperly. Always with the NMP charger. Never hot to the touch. Yes they were inside the airplane during the summer in the sun but I can't think of a battery that is not. John
2-4 years is most likely the shelf life on these things unless things have changed. I usually start seeing less flights and then its not long after i either replace them or only fly one -3 flights with them....