I switch back and forth from 2.4 to 72 and it's good to own the board these days but I still have to walk the line, there are two other pilots that still fly once in a while and we are all on 15, it's worth the walk in my case. I have been fooled by the modulation thing a few times, I still have several planes on 72 and one is on PCM and when I change planes I forget to turn my radio on and off to cycle it.
By all means go buy some new battery packs, after 10 years they may hold a charge for a while but they can go down very fast too. I take in my old packs to Batteries Plus and have them make up new packs for me. It's worth the price just to be sure.
I lost a plane last year and knew it was my radio having a problem, sent it into Radio South for service and my antenna was not making good contact so one minute all was fine and the next minute my plane was flying itself.
There can be several problems your system is encountering and it would be a good idea to let your instructor go through your system to try to locate it. On line help is pretty good but hands on would be a lot better.
