Any tips on how to store the spark controller? Like how many % battery it should be kept at?

I make sure to put a plastic joystick holder that has carveouts for buttons of the Spark Remote Controller atop, and I store it in the Fly More Combo Case. You can buy one on Amazon for under $10 that fits the Spark Remote Controller specifically.

I have not read a recommended percentage of power the RC should be stored.  I would think it's a different type battery than the Spark batteries.

This is all I can see about storing the RC, there's more on how long it takes to charge and how long it will run for but nothing on storing at less than full capacity.

In fact, to me it sounds like you should put it away at full capacity then as it says charge it up fully at least once every three months if it's not being used.

Here's what the RC manual says on Page 2 #6:
"Fully charge the battery at least once every three months to maintain battery health."

Happy Landings!

Please store the remote controller in a dry and waterproof place at a suitable temperature. Fully charge the battery at least once every three months to maintain battery health.