Another drain are the so-called CSS files that tell a browser how to layout the page. Again, on the Apple site, these required 12 joules to download and render onto the screen. Simple improvements reduce this by 5 joules.
Each joule might seem a trivial amount, but like a slimmer on a diet lots of small savings soon add up – especially when some websites take eleven times as much energy to visit as others.
But website design is not the only drain on a phone’s batteries. The way we access these websites – and in particular the settings our service providers use - also has a huge effect, according to Hari Balakrishnan, Fujitsu Professor of Computer Science at the Massachusetts Institute of Technology (MIT).
Surprisingly, it is the network that decides what power setting our handsets use. When we need to transmit, the network tells our handsets to power up to maximum. But the network’s interests are different from ours. We would like to power down again as soon possible to save our battery.
But only a slender portion of an already crowded radio spectrum is assigned for these so-called control messages, says Dr Balakrishnan. Because of that, the network tries to minimise the number of control signals it sends, even if that leaves our handset powering away while doing nothing.
“A classic example,” says Dr Balakrishnan, “is when you’re running an application that wakes up every 20 or 30 seconds and sends one byte of information. That would, in many cases, keep your radio in the high-power, active mode all the time. But it doesn’t have to. That kind of trivial workload should consume next to no energy, but ends up using huge amounts of energy because of the sub-optimal controls implemented by the networks.”
Like Dr Nicoara, Dr Balakrishnan decided to test his suspicion by wiring his battery to a meter and watching the battery drain. The results showed that by letting the phone control its own settings, he could halve the power consumed by the wireless transmissions with minimal effect on the network performance (although he stresses the details change from device to device, and from network to network).
Again, these might seem small improvements overall – but a network that can give our phones a few more hours of working battery life is highly likely to attract more customers these days.
Of course, it wouldn't matter how long your phone was fired up to exchange bits with the base station, if it could do so with minimal energy. But it turns out the mobile industry has been fighting a war with its electronics for years because they are so inefficient.
Specifically, it is the purity of the radio wave that they use to connect to the base station that requires so much power.
With radio spectrum restricted (see the two previous articles in this series) transmission frequencies are squeezed in close together, and any distortion in the signal would lead to catastrophic interference. And it turns out that the basic physics of the amplifiers that drive the antennae can only generate those pure waves when drawing a lot of electrical current.
When the 3G standards were introduced, manufacturers turned to a special design of amplifier first concocted back in the 1930s, because of the stringent demands of the networks. But even then, for every watt of transmitted radio power, there's more than another watt simply warming your handset to create this pure wave. Basically, simple physics is doubling the drain rate on your battery.
“The industry is racing furiously to mitigate this problem,” says Joel Dawson, Professor of Power Engineering at MIT, who has himself come forward with a smart fix that involves electronically compensating for this distortion, something that could apparently halve the losses. But how soon any of those fixes will make it to the market remains to be seen.