I'm not sure if I can independently charge the battery without it in the device; as of now I'm just charging it via the wall socket. I found charging it with a computer is slower.
It really doesn't matter. Technology today has gotten to the point where you're not going to irreversibly damage a smartphone battery by charging it unless it gets below a certain threshold...what is this, 1922?
Ideally you should let it run until it dies, charge it from 0-100, and repeat...but it really doesn't matter. Besides, these batteries will degrade after use no matter what you do. So best case scenario, you slow the degradation process down a little bit (13 months until the battery loses 10% capacity instead of 12 months). Don't let the worry of having to spend $30 on a new battery 1-2 months earlier than you would under optimal conditions force you into not charging when you have the opportunity to do so.