Better to go with an NiMH low self discharge cells commonly called "Eneloops". The direct replacement for your old NiCDs are 2000 mah cells, you can use your existing chargers and they work really well.
You can buy custom built ready to install packs from various vendors in the USA. While you'll occasionally see guys talk about putting in LiPO's, they were NOT recommended by Futaba and are a pain to charge. Some of the newer tx's use LiFE's but the pack shape is not the same so I've never seen a tx pack in an LiFE chemistry in a form factor that is compatible with your tx's.
Last edited by Zeeb; 10-30-2022 at 08:18 PM.