I don't see the purpose in leaving a battery on trickle charge for months but I'm no guru. Seems to me you're slow cooking them. Wouldn't it be better to let them discharge to a safe level (each cell 1 volt) and then charge them again? Just keep each cell above 1 volt while you store them. If you are using them every day, discharging them with a cycler or manually is what I'd do. Futaba recommends cycling battery packs in their manual. Charging indefinitly seems like you would over excite the battery and it would lose it's charging capacity sooner. Again, I could be wrong, it just seems like common sense to me. Do what you feel is right.

The other thing is how do you find out your battery is bad when using it for 7 years? Crash your plane? Will checking it under load (250 ma) every flight tell you if it's bad? I have an older battery and I just replaced it. I'm not taking chances. I even marked the old battery "for bench tests only..not running engines". I still want to keep it for setting up planes on my bench.

Joe