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I am not sure anyone has had same experience as I have. Recently bought a retina MacBook Pro and of course I was looking forward to enjoying the 10 hours of battery life that was promised.

2 months into the ownership I started paying more attention to the Energy Saver battery reading and to my shock discovered that the reading was fluctuating constantly.

No matter what I did I could not manage to get the 10 hours. For instance at one time it shows 8h 25 min battery power remaining, 30 minutes later it shows 5h 50 min power remaining. So I checked on the web and discovered had to shut down power hungry applications: bluetooth, WiFi, adjust brightness of the screen not to be too bright, I uninstalled Google Chrome and used Safari instead, turned-off keyboard lighting etc. This seemed not to have an effect on what I was experiencing.

Of course it would have been easier to go to the Genius bar but I first came across this Retina MacBook Pro battery life sucks? Here's how to fix it! web page.

However, before I could implement what is detailed there, I had temporarily had to move from my normal work desk to another room but same network. Then realised…my battery life improved enormously!! Then it hit me that the only difference was that in my normal place I connected to the internet via cable and in the new place was I using WiFi.

Surely WiFi should consume more battery than cable! Then I realised that in my usual place I used to connect via cable but through a Power Line Adapter (PLA).

So my questions are:

  • How do these power line adapters work?
  • Why should they affect battery of my laptop?
  • Should I continue using a the power line adapter with the laptop?

There is no information of this from the manufacturer of the power line adapter and have yet to get Apple's opinion on this.

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How do Powerline Adapters Work?

Powerline Adapters are, in effect, baluns1 that embed an RF frequency on electrical wire. What they are doing is taking the unbalanced CAT5 signal (which requires a ground connection) and converting it to a balanced RF modulated signal that is transmitted over the building's copper electrical wiring. At the other end, it does the opposite to convert it back to CAT5

Why should this affect your battery?

The powerline adapter doesn't affect your battery per se. What affects your battery is how much power is required to make your connection and how much traffic you send/receive. The more power required, the less life on your battery.

Ethernet (CAT5) is designed for "high speed, long distance, and high reliability (noise immunity). All of these features generally require trade offs in power consumption."2 Additionally, if the SNR (Signal to Noise Ratio3) is high, it will increase power and/or lower transmission speeds to accommodate

WiFi is basically the same but with the benefit that it will adjust its power based on the quality of the signal unlike Ethernet. Where your signal is excellent, your WiFi adapter will lower its transmission power as extra power would simply be a waste. Where the signal quality is poor, it will increase the transmission power to ensure connectivity.

This is also why your cell phone's battery also doesn't last when the signal is weak.

Conclusion...

In your scenario, you may have a WiFi signal that is excellent and for the work that you do, you don't see an impact in terms of speed or reliability going over WiFi. Your upside is longer battery life.

However, should you have the need for higher speeds (like "moving" vast amounts of data), WiFi simply won't keep up with the transmission requirements. CAT5 will be the advantage here. Whether it's on a power line adapter or on a switch will not change the power consumption of Ethernet.


1Balun - Balanced/Unbalanced. A device that links together dissimilar wire types and attempts to minimize any negative effects to the signal that would normally result from the dissimilarity. Dictionary of Networking Terms

2 Microchip - high power consumption in ethernet mode

3 In an electromagnetic signal, the ratio of the amplitude (strength) of a signal to the amplitude of the ambient radiation and other signal disturbances that are present, usually expressed in decibels (dB). Dictionary of Networking Terms.

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