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The battery life on modern portable gadgets is much lower than ten or twenty years ago, mainly because electronics technology is developing much more quickly than battery technology. Batteries are struggling to keep up with all the amazing new things that portable gadgets are capable of.

With this in mind, it's important to use a portable device's battery as efficiently as possible. This tutorial will look at some simple ways to do this on the Nokia tablets. The point is to put the most effective measures first but it can't be guaranteed that it compares straight to reality. There are too many scenarios for every aspect to keep the order always 110% right.

Before reading on, have a look at the N900 User Guide on your tablet, and read the section '''Prolong battery life''' in the chapter '''Find help'''.

== Do not put your device in a pouch with magnetic clasp ==

This is a rather odd problem, but is actually quite common. It is alone sufficient to spend a fully charged battery in less than a day.

The keyboard slide is detected by a magnetic coupling and nearby magnets may confuse this function. So if you put your device in a pouch or jacket pocket that uses a magnetic clasp, the device might believe that the keyboard is opened and closed all the time.

== Don't have 3G enabled unnecessarily ==

This applies more to the [[Nokia N900|N900]], but if you use a 3G-enabled cell phone to connect your older tablet to the web, this tip should help your phones' battery life.

Even when you would have a good 3G coverage, turning the connection to GSM only will help battery life immensely. Your connection speed will slow down if you do it, but not as bad as you would imagine. The phone will use EDGE speed (2.5G) which is 384 kbps at theoretical maximum. This is in many situations sufficient. 

Turning off 3G will help your battery life even more under spotty or non-existent 3G coverage when the phone doesn't have to search for the 3G connection all the time.

There is a [http://maemo.org/packages/view/3g2g-mode-selection-applet/ small status bar applet] that lets you switch easily between full 3G and GSM only. Using such an app lets you mostly have the phone in GSM mode for background tasks, and switch to 3G only when you actively use the internet.

Many users find that they have about 50% battery left after a full day's worth of usage if they only use 3G when really needed (and don't have the magnetic clasp problem).

== Turn down the screen brightness as low as you can cope with ==

One of the '''major sources of battery drain''' on a portable device is the screen. If it's very large and very bright, it will use up a lot of battery life when it's lit.

One of the best things you can do to save battery life is to turn down the brightness on your tablet's screen to the lowest level that you feel comfortable with. The lower it is, the more battery life you will save. Just click on the screen brightness icon (the icon that looks like a sun in the status bar at the top) and adjust the brightness on the sliding scale.

For Maemo 5, you can use the [http://maemo.org/downloads/product/Maemo5/simple-brightness-applet/ Simple Brightness Applet] (available in Extras) to have easy access to the brightness controls.

== Make the screen dim and switch off as soon as possible when not in use ==

Like all portable gadgets, Nokia's internet tablets have an automatic dimming and shut down period on their screens. If you don't use a tablet within a certain time period, the screen will dim, and if it continues to be unused the screen will switch off. You can make it switch back on at any time just by touching the screen.

To get the maximum battery life, set the time-out period for screen dimming and shut down to the shortest possible time. To do this click on the brightness icon in the status bar (the one that looks like a sun at the top of the screen), click on "Display Settings", set Brightness Period to 10 seconds and Switch Off Display to 30 seconds. Click "OK".

If you get annoyed by how quickly the screen dims or shuts off, you can always increase the Brightness Period and Switch Off Display time until you feel more comfortable. However, this will use up more battery life than the minimum times.

[http://maemo.org/downloads/product/Maemo5/simple-brightness-applet/ Simple Brightness Applet] has a very convenient way to keep display on without timeout: just click and hold the rectangle "screen" icon on left side of slider

== Switch off Bluetooth when you don't need it ==

The Bluetooth wireless system is intended to let the tablet easily connect to nearby accessories or computers, but if you're not using the connection then it's worth switching it off to avoid it needlessly wasting battery life.

Bluetooth doesn't use much power in standby mode (some 2..3mA) so this may not have much of an impact on battery life, but if you genuinely don't need it then there's no point having it switched on. Tests proved that BT doesn't use any significant power on N900 when set to active+'''invisible'''.

To switch off Bluetooth just click on the status bar at the top (or open the system-settings dialog), click on "Bluetooth Settings", and tick or untick the box marked "Bluetooth On". Click "OK" and the Bluetooth will switch on/off accordingly.
The very next checkbox in the same dialog is for selecting visibility status of BT. Setting it to "off" (aka "not visible") will make BT not send own name all the time, thus saving part of the above mentioned power consumption of BT.

== Switch off Wi-Fi when you don't need it ==

Again, like Bluetooth the Wi-Fi wireless standard doesn't actually use that much power when it's in standby mode (but there are still some nasty bugs in the wifi subsystem that can drain your battery in an hour, like https://bugs.maemo.org/show_bug.cgi?id=6615), but if you really don't need the Wi-Fi connection then there's no point having it switched on.

To disconnect Wi-Fi, just click on the connection icon in the status bar at the top (it looks like a small ball with curved lines radiating upwards) and then click on "Disconnect". Click "OK" and the Wi-Fi connection will be disconnected.

To re-connect, click on the same icon, then "Select Connection", then click on the connection you were using before and press "Connect".

It's worth noticing that the WLAN chip is using considerable amounts of battery energy during scanning for APs. This is where the setting for scan period becomes relevant: set it to a period as long as acceptable for your usage patterns. A scan may easily take longer than 60 seconds, during which the WLAN chip is consuming full power, so for shortest "search interval" setting in "settings -> internet connections"  of 5 minutes you have a so called duty cycle of 60/300 = 20%. Do your math for search interval = 30 minutes.

== Turn on Wifi power saving mode ==

{{main|Wifi power saving mode}}

The Nokia tablets support power saving mode (PSM) for wifi. You can find out more about how to turn it on, and the positive and possible negative consequences in [[Wifi power saving mode|this page]].

== Don't switch off the tablet! ==

Yes, that's right, if you want to save battery life then do NOT switch off the tablet when you've finished using it.

You can charge it while it's switched on, and if you want to carry it you can lock the touchscreen and keys so it doesn't accidentally activate anything while in your pocket or bag.

Leaving the tablet on to save power might sound absolutely insane, but it does work apparently, and there are good reasons why it works.

When you switch on any modern computing device such as a PC, smartphone or pocket computer, it has to go through a complex and intensive process of getting the device ready for use. This takes a lot of effort by the computer, and anyone who has booted up a PC knows how long they have to wait between powering up and actually getting to use it. This effort uses a lot more power than simply staying switched on doing nothing.

If you switch off your tablet and then switch it on a few hours later, this apparently uses up more battery life than just leaving the tablet switched on for several days. For this reason, it saves energy if you leave your tablet switched on all the time, just like you'd leave a mobile phone switched on all the time.

== Use Offline Mode (aka Flight Mode) ==
'''N.B.''' Calls and texts cannot be made/sent or received in these modes, so ensure call-forwarding is active before enabling either flight- or tablet- mode.

===Offline (flight) mode===
A quick and easy way to shut down the tablet's radio transmissions (ie. WWAN aka GSM, Bluetooth and Wi-Fi) is to put the tablet into offline mode, which is the same thing as flight mode.

To do this, press the power button briefly so that a menu appears, click on "Offline Mode", click on "OK" as necessary, and you will be in offline mode.

To get back to normal mode, just press the power button briefly again, click on "Normal Mode" from the menu, click on "OK" as necessary, and you will be back in normal mode.

The reason this is also known as flight mode is because many airlines have a ban on passengers using devices which transmit radio signals (including phone signals, bluetooth and wi-fi). If a device is in flight mode it does not transmit any radio signals, so many airlines will allow its use in this mode.

This is useful also at night if you don't want to be disturbed by messages etc with N900. Just put it to flight mode when going to sleep and online when you wake up. No need to be afraid that silent mode has the alarm too silent etc.

===Tablet mode===
Traditionally, tablet computers have no GSM/GPRS/EDGE/UTMS/etc. connection but can connect to wifi, bluetooth and hardware connections. Tablet-mode replicates this by preventing phone functionality and preserving access to other connections. Therefore, tablet-mode reduces battery consumption compared with "normal" mode, yet allows some connectivity. As such, it is a useful alternative to the complete blackout of flight-mode, even though it is not quite as power-conserving.

For the N900 (Maemo5), Cellular Modem Control Buttons [http://maemo.org/downloads/product/Maemo5/cell-modem-ui/ V0.5.1-1] is available in -extras; its package name is "cell-modem-ui". This software allows tablet-mode to be en/dis -abled in the same way as flight-mode: from the power button menu.

== Replace your SIM card ==

As it turns out, an old SIM card will have a lot of scratches on its pins. Some of them may even be bent inwards or otherwise damaged.The SIM cards are not designed to last more than couple of years and they really should not be taken out of the phone frequently as this damages the pins.

Long story short, old SIM cards "leak" power due to bad contacts and increased internal resistance [''citation needed'']. In addition, other users have mentioned that depending on their age, different SIM cards operate in different voltages (5V, 3V, 1.8V). The N900 has support for legacy SIM cards which means older SIMs will require more power.

The operator probably will give you a new sim for free if you ask kindly.

== Shut down any applications you're not using, and be careful when using unofficial applications ==

If you have an application running in the background, this uses up battery life. If you're not using an app, it's a good idea to shut it down (or "kill" it) using the task icon in the bottom left hand corner of the screen: just click on it and click on the X next to whichever app you want to shut down.

Some applications, especially unofficial ones, may use up far more battery life than they're supposed to because they're badly programmed. If you find that your tablet's battery life has suddenly turned to mush since you installed an application even though you don't use it very much, bad programming in the application may well be to blame. The easiest way to check if this is the case is to remove the application and see if the battery life improves.

Most applications work fine and don't mess around with battery life, but some do, and it's this minority that you have to watch out for. One pretty notorious 'candidate' is skype!

== Adjust refresh rates for apps that fetch data from internet ==

This appliese to every app that has a setting for refresh rate. Do you really need to have every time max 29 minute old weather forecasts or could you cope with 2 hours old data? What about fetching email every 15 minutes, what if you would get mail once in a hour? And one can always manually poll the mailbox when needed.

== Remove Widgets from desktop ==

It probably isn't very great idea but if you need to really optimize battery life, you should remove every widget.

But every time a widget refreshes it's display, it uses the processor and consumes battery.

== Trim mailbox ==

If your mailbox has 50 folders, it will slow the fetching and therefore consume much more battery.

== Know how to spare batteries ==

The batteries wear out eventually. To increase using time and see some tips when buying new batteries, look through [[batteries]] article first. It has a lot of useful information. Also, charge up when you have the chance.

If you really need to stay out long with your device without a chance to charge, invest in a spare battery. These are even available with standalone chargers on eBay, so you can charge the spare battery while using your device with the other battery.

== Check your profile settings ==

Do you really need your phone to vibrate and play a sound as loud as possible when an email is received? Or could the notification light do the trick fully?

This is also very minimal amount of battery drainage but still worth considering.

== Observe your usage ==

Some of these techniques are more efficient than others, and some affect the user-experience more than others. Try out different combinations to improve your battery life, but don't compromise too much. Find the best way for your own usage and keep your device usable!

There are good apps to help you keep tabs on your battery usage profile like [http://maemo.org/downloads/product/Maemo5/battery-eye/ Battery-Eye] that shows a history-graph of your battery levels and has some nice usage statistics, [http://maemo.org/downloads/product/Maemo5/batterygraph/ BatteryGraph] that shows everything Battery-Eye shows and can show the state of use of your processor in each time (thus showing any leakage of processing by an undesired program), so that you can see if you really have a bad process running in background and [http://maemo.org/downloads/product/Maemo5/conky/ Conky] that (among other useful things) shows your current CPU load and the most CPU-intensive apps running at the moment. All are available from the [[Extras|Extras repository]]. Take care since all those monitor apps are usually quite CPU heavy and thus power hungry by themselves - all the info shown has to get acquired first, and then depending on app it needs frequent complex rendering and display updating.

== Perform power-saving actions on phone lock/unlock ==

One of the simplest uses of [[DbusScripts]] is to detect when the phone is locked or unlocked and run scripts to reduce the cpu frequency, system load, etc.

=== Suspend user processes ===

See Xagoln's post: http://talk.maemo.org/showpost.php?p=1005668&postcount=1

=== Change kernel powersave bias ===

Over on the [[Overclocking]] page, Fecn describes a set of scripts to modify the [[Kernel Power]] settings on phone lock/unlock, basically to underclock the CPU (or at least, undo overclocking it) whilst the device is locked.

Note that this is '''contrary''' to the general "rush to idle" policy used maemo [http://www.phoronix.com/forums/showthread.php?27539-Ubuntu-Faster-But-More-Power-Hungry-Than-Mac-OS-X]

== Use the Kernel for Power Users ==

Not just for [[Overclocking]], the [[Kernel Power]] package helps to save battery power and makes it easy to configure CPU frequency scaling. You should be using this for power saving purposes even if you never choose to go over the stock 600 MHz.[''citation needed'']

=== Enable SmartReflex ===

[[Smartreflex]] is stable up to 900Mhz with =>KP50 (recommended)
Having both VDD1 & VDD2 enabled will increase your battery life. [''citation needed'']

=== Powersave bias ===

The powersave bias setting modifies the behaviour of the ondemand governor to save more power by reducing the target frequency by a specified percentage. This can be used to limit the extent to which the phone will overclock, according to user-specified criteria.[''citation needed'']

== links ==

http://wiki.maemo.org/N900_Hardware_Power_Consumption
http://wiki.maemo.org/N900_software_power_management

[[Category:Users]]
[[Category:N900]]