I bought a 15" mid-2012 Macbook Pro second hand earlier this year. It's in great condition and everything works perfectly. However, I've noticed that the batter seems to drain pretty quickly - after constant use for 2.5 hours, even when screen brightness is minimal. it'll be dead and I have to recharge it. I've done some research and found that the battery should be expected to last up to five and a half hours. I know that this would be based on a specific way of using the macbook, but 2.5 hours seems a bit short regardless. Basically i'm wondering if the previous owner has switched out the original battery for an aftermarket version that isn't as good, or if it was because the CPU is using too much power due to too many programs being open, etc. Is there a way to check for serial numbers or anything if I open up the back panel and take a look inside?