I'm going to travel soon, where the access to the electric grid can be spotty and I don't want to put any additional strain on my iPad battery, by f.ex. charging a pencil - so, if I charge the pencil 100% before leaving, how long can the charge hold without using? Can I like charge it fully, then not use it for 2 weeks while travelling and then still be able to use it after the two weeks without re-charging? In other words how long does it take for a pencil to discharge on its own without use?