RE: 2.4 conversion & unstable voltage indicator
I had this exact problem with a 10X. I even called Horizon and they said that the 2.4 module was proabably dying. I just didn't quite buy it since a few months earlier it was fine and it sat in the case. The 72 module worked fine, and voltage was steady without any module. I took the battery out of the cassette, wired it to a plug and put it in my old 8103. Same results, 72mhz fine, 2.4, voltage all over. Seems like slam dunk, bad module... especially since the battery pack cycled within 10% of capacity with a C/10 mah discharge. Each cell checked perfect on voltage.
I still had a hunch something was off. I wired up another battery to the 8103, all is well. Wired the same battery to the 10x, no problems at all. I flew with it, no issues. I started checking the cells' resistances. One cell had a super high reading compared to the rest. I surmised that that the one cell was just not passing current to the module and thus the low and fluctuating voltage readings.