Is it okay to always charge it? Like when the battery is still at 50 - 90 % when i see an AC outlet i will charge it right away and remove it even it is not fully charged.
I am not an expert, but based on what I've read in other forum responses, lithium ion batteries like to have some exercise to keep them healthy, just like us humans. So charging more often, prior to the battery getting too low, doesn't hurt it and might even be a benefit. The most important thing, though, is don't worry very much about the battery, but instead have fun with your N7! You'll likely be ready for an upgrade long before you have any battery issues, regardless of how you charge it.