There are three considerations to that question
1. It's generally NOT best practice to keep lithium
batteries fully charged. That is why the smart
batteries in the drone will purposefully discharge after a few days in storage. Keeping them at or near 100% will shorten the life of the
battery.
However...
2. The degree to which the
battery life is shortened is tiny compared to the inconvenience and risk of the controller dying during an outing or mid flight.
And...
3. The RC
battery lasts A LOT longer than the aircraft
batteries (about 10 to 1 in my experience). I have 3
Spark batteries that I use during each outing. After 2 outings (6
batteries used) the RC is usually down to 30% - and that's when I charge it. This is easy to remember, safe and gives the
battery a good cycle.