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.
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.
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.
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”.
