If your present charger doesnt support A123 then you will need a new one.

A123s are nearly half the weight of nicads, but you can do a voltage check on nicads to see "how much is in the tank".

Both are the most bullet proof solutions for receiver packs.

On my 50cc I have a 1200mah nicad on ign and a single A123 2300mah for receiver. I will soon run both off one 1100mah A123. I have a fromeco badger switch that is failsafe and has charge port so it is easy to charge every two flights. One 1100mah A123 weighs 95g. separate nicad packs including what you have would weigh over 500g. CLose to a pound saved.