Zagg powersparq store at 40%

[moot]

How important is it that I leave my sparqq at a 40% (recommended by instructions) charge during long periods of non-use?

I've left it in my bag for the past couple of weeks at 100%. I would charge it down to 40%, but I am concerned that at some point I may need the full 100%, when I am away from a wall outlet.

Thanks