I was playing Final Fantasy XIII-2 for hours and I saw that my controller had a single bar of battery life left. I told my neighbor my problem and he told me he had a Xbox 360 Rechargeable Battery Pack. I checked for the price of the latter and I can't afford them. Do I have to buy this pack for my controller or do I just have to buy new batteries?
Firstly, you can find the battery slot on the back of the Xbox controller
It depends on the type of battery pack you do have. If you have a rechargeable battery pack (depending if you got it new or second hand) it should have come with a recharge cable. This is what it looks like:
If you have a normal battery pack, all you need to do is replace the batteries. Two AA batteries will work, rechargeable or not will both work (I'd suggest rechargeable - bit more expensive, but you won't need to buy more!).
Pictures not to scale.