I found a bluray disc of Battlefield 3 without the box. Will I be able to install it on a PS3 without a box/key or do I need a serial key that might have been on a box?
I just looked at my box and there is no serial key on this game you should be fine to install it. There were several games with online codes in this era but this does not appear to be one. At most you might miss out on a promotional item that is no longer valid due to those having expiration dates on them.