Toy transmitter steadily losing range

My transmitters appear to be wearing out. Im pretty sure its not dead batteries, I didnt buy tons of batteries and pump them just to be sure, but I have tried fresh batteries at similar troubles over recent times,. I have two toy drones that seem to have steadily decreasing range. Is something wearing out? Could they need "factory resets" the range issue is always consistent for several drones to the same controller,, and I promise I have eliminated batteries as a cause. What could be causing my drones to lose signal more frequently as they age? (Brand new copters work fine)

 

I would open the TX and inspect the antenna, I has one that scrunched back on itself. Once I straightened it out things improved. You could also open a TX that works fine and compare the antenna arrangement.