Four hour battery life on new MacBook Pro Retina?

Hey everyone! I just bought a new 15" Retina MacBook Pro a few days ago and I'm having issues with the battery. For some reason, I can only get around 4 hours on a charge. All I've done so far is install a few programs, browse the internet and listen to music via spotify. But still I'm not getting any battery life. I thought there was an issue and so I brought it back to the Apple store. They took it overnight and ran a diagnostic on it and told me that everything is normal battery-wise, and the specs look like they are fine. They also charged it fully and let it run with activity monitor open and they said it lasted around 7 or 8 hours. But still the time remaining is telling me sub 5 hour times. I installed Battery Health to see if there was something I was doing wrong. It tells me I'll get around 7 or 8 hours internet browsing, but my current usage is only around 5 hours. What am I doing wrong? How do I fix this?

My specs are as follows:

15" Retina MacBook Pro

i7 2.3 gHz Processor

16 Gb RAM

512 Gb SSD

Nvidia GeForce GT 750m

Side note: Is there any way to back up my computer online or is it best to do it via harddrive? And also any other tips or tricks you can offer to me? This is the first Apple computer I've ever owned and I'm still trying to find my way around the OS, especially with using Finder.

Thanks!