NiCads self discharge 1 or 2% per day just sitting around. The AA size cells are 1.2V, and eight of them are 9.6 volts. As your TX meter shows, you've actually overcharged them (which is normal as they get a 14V "kick" from the wall wart. That overage goes away much faster than the plateau voltage will. My 9C "normally" reads 10.6v whan I get to the field, and I keep all my Tx & Rx on a timed charger that hits them with 15 minutes of charge every day to keep them topped off. What is scarry is that a 9.4v cell is about done and shouldn't be flown, but a 9.6v cell may have 80% of it's flight time left. The voltage alone doesn't tell you much.

Invest in a digital read-out charger/discharger (i.e. the Hobbico Accu-Cycle) and an ESV (expanded scale voltmeter). They put a load on a battery and tell you how it is doing.

I'd guess 3/4 of "accidents" where pilots claime to have been "shot down" are because of battery problems. They wear out and require maintenance like anything else.