You've got plenty of juice right now. Your current reserve lets you use your keyboard in total darkness for three months - so you can type all you want.

Want to keep your energy reserve high? Expose your keyboard to enough sunlight or indoor light even when you're not using it. (Don't worry - it recharges with light even when it's switched off.) Your best bet is to keep your keyboard no more than 9 feet (3 meters) from a window with a direct line of sight.