i use lithium ion in all my jets for receiver and ecu with a few planes having lipos on the ecu that i can get to easy for charging outside the plane,i guess the new down side to ions is the regulators and the fact that you can't hard charge them at the field but then again i have never had to charge a ion in good condition getting 5-6 flights with two 2600 mah packs on the receiver,i do like the a123 batteries just have heard and seen a few guys have trouble burning up servos with them when freshly charge