How To Get The Best From Your Batteries (Part 2)

11/30/2012 3:50:47 PM

Maximizing laptop battery life

It's natural to want the longest possible battery life from your laptop. If you have a modern thin and light model in which the battery is integrated into the body and can’t be replaced, you'll want to maximize its lifespan; too, since replacing it means sending it away and probably facing a hefty bill.

As we've mentioned above, the best way to do this is to avoid completely emptying the battery between charges - so in all cases what's really wanted is a way to make a charge last as long as possible.

Description: laptop battery

Laptop battery

The Power Options in the Windows Control Panel (called Energy Saver in OS X) let you control various settings, such as how long the computer should sit idle before automatically dimming its screen, spinning down its hard disks, going to sleep and so forth. Such measures are helpful if you're using the computer sporadically, but do nothing to prolong battery life for a PC in constant use.

Happily, there are several things you can do to increase the battery life of a PC while you’re using it. The most obvious one is to keep the screen at a lower brightness level. This is a great way to save power, as the LCD panel is one of the most energy-hungry components in a laptop, yet it doesn't affect the practical performance of your computer at all.

Many laptops progressively dim the screen automatically as the battery depletes, so as to eke out the remaining charge. You can get a greater benefit by dialing back the brightness of your screen full-time, perhaps turning it up only when bright ambient light makes things hard to read. The effect will vary from system to system, depending on the particulars of the hardware. We tested an Asus N55SF laptop (with the battery disconnected) and found the whole system consumed 20W when sitting idle with the screen at full brightness, but only 15W at its dimmest.

Another power-hungry component is the processor. When under heavy load, the CPU is by far the most demanding part of the system - this is when it may approach its maximum Thermal Design Power (TDP) rating. We tried stress-testing our sample laptop, taxing each of its four cores (plus four virtual cores provided by Intel Hyper-Threading) with 100% load: power draw rocketed from an idle rating of 20W to a steep 75W. Since the supplied battery is rated at 56Wh, expected battery life under this type of load would be a mere 45 minutes.

Clearly, it's best to avoid running heavy number-crunching processes on battery power. You may even choose to throttle the maximum CPU speed in Windows' Power Options - and it's worth having an audit of your startup items to disable any unneeded programs that run in the background and keep your CPU churning needlessly. See last month's discussion of tune-up utilities for a guide.

If your laptop has switchable graphics, you can save power by ensuring the discrete GPU is disabled and steering clear of 3D applications, as these devour power at a great rate. You can cut a few additional watts by disabling unneeded wireless features such as Wi-Fi and Bluetooth; disconnecting USB peripherals that draw power from your PC; ejecting discs from optical drives, which may otherwise periodically spin up; and even turning off unnecessary lights such as keyboard backlights. We can't promise any of these measures will give you more than a few minutes of extra battery life, but at least you'll know you're not wasting power.

Finally, if you need to use your laptop intermittently, consider setting the default sleep mode to hibernate instead of sleep. This switches off the computer completely, so it will take a bit longer to resume, but the battery won't be depleted while you're not using it.

Maximizing battery life on phones and tablets

It's a frequent complaint that mobile phone batteries don't last as long as they used to. A few years back you could expect a charge to last for three or four days on end, whereas now it's the norm to recharge every night. Indeed, it's a catch-22 situation, since running down the battery in this way inescapably leads to a progressive reduction in capacity over time.

Description: mobile phone batteries

Mobile phone batteries

Battery technology hasn't regressed, of course; rather, phones have become much more demanding, with vastly more powerful CPUs, huge screens and dozens of processes running in the background at all times. Effectively, they're little computers - as are tablets. And for both types of device, you can save battery life in most of the same ways: dimming the screen and turning off wireless and Bluetooth connections when they're not needed, as well as the GPS receiver, for example.

On a smartphone, you can also reduce the amount of power used by the radio unit by preventing apps (and system features such as Google Play and Gmail) from automatically polling for updates, or making them do so less frequently.

Android users may choose to install a battery-saving app that will automatically switch various features and services on and off to a schedule - one example being the free JuiceDefender app - so they're available at times when you might want them but not wasting power when you don't. Unfortunately, Apple's developer restrictions mean this isn't possible in iOS.


Android also supports a range of "task-killer" apps, which automatically close programs running in the background, but here the benefit is likely to be minimal: Android apps (unlike Windows applications) are largely suspended when not running in the foreground, so there isn't much to save. Indeed, if you end up repeatedly relaunching closed apps, this can consume more power than leaving them running in the first place.

A final tip: as with laptops, do your best to keep phones and tablets cool - for example, by avoiding leaving them in hot cars in an Australian summer. Heat will quickly erode the battery's life - and, in many cases, there's no easy way to replace a rundown battery.

Reducing power consumption

Modern CPUs are designed with a strong focus on cutting power consumption, so as to make the most of each battery charge. It’s no exaggeration to say that energy efficiency is a bigger concern for chip-makers than performance: Intel CTO Justin Rattner last year set a goal of cutting PC power requirements by a factor of 300 in a decade.

This will be accomplished through a variety of energy-saving measures. First, the regular “die-shrink” process - wherein existing CPU architectures are physically reduced in size - will continue to reduce the scale of electrical leakage, allowing the same amount of work to be done with less power.

Description: Reducing power consumption

Reducing power consumption

Recently, Intel has also been building extensive power-gating capabilities into its chips. This divides the chip into dozens or hundreds of isolated “power islands”, each of which can be turned on individually as needed, and switched off again when its function has been completed. The thermal image below shows how, in its fully gated state, the chip is almost entirely cold, indicating most of it is unpowered. This can reduce the chip’s overall power consumption significantly when doing something simple such as writing a word-processing document.

The CPU is, however, only one component of a laptop - so there’s a limit to how much power can be saved in this way. Intel is therefore working on more ambitious plans, too. CEO Paul Otellini announced last year that the Haswell micro-architecture, due for release in 2013, would introduce a “system-level power- management framework”.

Details remain under wraps, but we expect to see motherboard components such as USB ports, audio outputs and network adapters powering down when not in use. Otellini has promised that Haswell’s power-saving systems will enable laptops to deliver “all-day usage, and more than ten days of always-connected standby, on a single charge”.

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