Battery

Not had my Android for that long, I did charge the battery fully before using even though it showed that the battery was halfway to being full.
I don't think that I needed to charge it fully, I could have use the phone right away.

 

I use my phone right out of the box, then charge the battery fully after I've ran it dry.

 

You have to charge the battery fully, leave it for a few hours after it's fully charged, then let it die completely before charging again.

The initial few (and importantly the first) charges set a precedent and it teaches the phone what a full charge should be. Not doing so could potentially have a negative impact on battery life for the rest of the time you have your phone.

It's the same when you switch a ROM, you need to recalibrate the phone/battery so that it knows how much is 100% charged.