You will find out testing your cells without a cycling type charger is time consuming and not very practical. If they are three years old and especially if they were purchased at Walmart then I would pitch them just as far as you can, no ifs ands or buts.

Another problem if it was modified with some sort of spring contact holder for the individual cells then that is another liability that can and will fail at some point. I would never use that kind of cell holder in any kind of airplane. They can corrode and cause problems and lessening tension as the box cracks or bends is another failure mode that is common.

Yes, in this application Nimh is a better choice now and you can get high capacitys up to about 1600 mah. There is no reason you cannot get good ready made packs to fit that tranny in many capacitys. Please get rid of that Spring box.

Your Tx and Rx flight packs are the very last place to start scrimping a buck, some of the home brew battery packs that I have seen are simply horrifiying and most have failed in some way.

John