Charging Hatsan cylinders outside of rifle.

I have a Bullboss and have been removing the cylinder it to charge it up. I have never left it in the rifle while charging. Is it ok to keep doing this, or is there a reason to sometimes leave it in the rifle to charge.

Also how long can I keep the cylinder at max pressure? Should I store them at a lower pressure? Longer than 1 month without use.
 
I keep my Gladius fully charged. One added benefit is a cylinder that is charged with air that is dry(I’m assuming my compressor dryer and filter are working) you won’t have to worry about condensation forming inside. I remember from scuba diving we were trained in the Navy to never leave a tank empty to minimize condensation.