I recently got an iPhone from a friend. It's not new, and he used it for like two years before he purchased a new iPhone. Appearance-wise, this 4s is still okay. No scratches whatsoever. It even has the original charger, earphones, and box still. Unfortunately, the battery life isn't so good. I noticed that unlike other iOS devices, this iPhone drains in about three hours. I searched online, and guides told me to update the OS. I did, but it still doesn't last too long. I wonder if anyone here can tell me what I should do to make my phone's batter last longer. Greatly appreciated! TIA!