Lithium batteries gradually lose capacity with age and use.
You can check to see how much capacity has been lost in the battery settings in the app.
Compare the capacity of a freshly charged battery with the number printed on your battery label...
If you need a controller, I have several.
You could also try a camera calibration and see if that makes any difference.
Could also be some debris in the gimbal motors slowing things down. Some form of air blowing that out possibly?
You mention the RC1A/B controller losing stored charge at an accelerated rate and not being able to charge it higher than the mid-90% mark.
If you charge it as fully as it will allow and then shelve it without use for 24-48hrs, does the level of...