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.

  • 1
    (Rhetorical). Why is the 2017 Toyota Corolla (subcompact) fuel efficiency so much better than than that of a Toyota Highlander (crossover)? Let’s forget for a moment that we’re talking about two very different machines, why would tech not improve over 4 years making things more efficient?
    – Allan
    Mar 25, 2020 at 18:19
  • @Allan but are they really that different? They're only three years apart. Running the same OS. And my battery is brand new. Mar 26, 2020 at 9:45

1 Answer 1


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.)

  • Right, this is a combination of factors. New MacBooks are much more efficient, especially on standby or low-usage power consumption. OP, you should consider moving to a newer MacBook if you want better battery life, that's really the only way
    – Oion Akif
    Mar 25, 2020 at 16:20
  • The serial number you quote is for the Battery Controller chip which would be the SN# of the battery itself because you can’t embed nor read code from the actual battery
    – Allan
    Mar 25, 2020 at 18:27
  • @Allan - In System Information > Power, the very first item is a unique serial number for the battery. Then there's the Manufacturer, then the "Device name", which is bq20z451 on lots of Macs. Including my own!
    – benwiggy
    Mar 25, 2020 at 18:48
  • Ok. And? It’s not stored on the actual battery itself. Your rebutting a point I didn’t argue.
    – Allan
    Mar 25, 2020 at 18:50
  • Not sure I understand then, but hopefully I've edited the answer to clarify.
    – benwiggy
    Mar 25, 2020 at 18:59

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