Why is 2017 MacBook air battery life so much better than 2014 MacBook pro's? Why is my girlfriend's 2017 MacBook air battery life so much better than my 2014 MacBook pro's (after just having brand new battery installed) when the batteries have the exact same device name (bq20z451)?

Format: her computer/my computer 


Processor: 1.8GHz i5/2.2GHz i7 
Full Charge Capacity (mAh): 6540/8230 
Cycle count: 628/10 
Device Name: bq20z451/bq20z451


Hers is notably better, maybe about 2x better. No, I'm not storing or editing insanely big video files. We both run code but haven't done much of that recently.

I calibrated my new battery and it helped but just not that much.

I dropped £199 on a new battery and I wanted an absolutely sick battery but I'm really disappointed in this. Yes it's better than it used to be but nothing like when I first got the machine.

Does my 2.2GHz i7 processor really drain it 2x faster? Why would it matter if neither of us is maxing out the CPU anyway? Maybe my bigger motherboard is more demanding even when idling but really is it bad enough to account for this drastic of a difference? Bluetooth is off in both cases.
You have the 15" 2014 MBP, judging from the CPU speed. So you have an older CPU that uses more power; four times the number of pixels to push; and older battery tech. On the plus side, you have a larger capacity battery.

Your MBP requires an 85W charger, and the MBA uses a 45W charger. So that's indicative of power consumption.

Apple advertised the 2014 MBP at 8 hours of wireless web usage; the 2017 MBA is rated at 12 hours. So you should see 1.5x on the MBA.

I have the same model of MBP, and also recently got the battery replaced. I get about six hours using audio apps, Xcode, DTP stuff, etc.

The Device Name bq20z451 you quote is the model of the Battery Controller chip, rather than the serial of the battery itself, and is the same across a wide range of Macs with different battery characteristics. (Every battery also has a unique serial number.)