BU-809: How to Maximize Runtime

Discover simple tricks to lower power consumption and extend runtime.

As the author of BatteryUniversity.com, I get many interesting enquiries from battery users. A man writes, “Hi, I am looking for an answer to a perplexing question. A co-worker and I have identical cell phones from the same provider. Moving into a new house, she complained of short battery runtime. I told her she was out of her mind, but then I noticed my battery behaving differently when I travel. Is there some mysterious force that’s draining the battery?”

Yes, there is a hidden force that drains the battery but it’s not mystical. When a cell phone is in constant communication with the tower, it transmits small bursts of power once every second or so to check for incoming calls. To save energy, the signal strength adjusts the transmission power and only consumes what is needed to maintain communication. If the cell phone is close to a repeater tower, the energy required to communicate is very low. Moving farther away or entering an area with high electrical noise, such as a shopping mall, hospital or factory, and the required energy increases. An analogy is sitting in a restaurant. When the surroundings are quiet, the voices are kept low and as the crowd grows everyone needs to talk a bit louder.

Living in sight of a tower has advantages and your battery will last longer between charges. Where you park your mobile phone in the house also affects runtime. A manager of a large cellular provider in the UK said his son experienced shorter standby times after moving from the upstairs bedroom to the basement. If possible, leave your mobile phone in an upstairs room facing a tower. When traveling by car place it near a window rather than on the floor but avoid direct exposure to the sun.

Similar rules apply to TETRA and P25 radio systems, cordless telephones, Wi-Fi and Bluetooth devices. A wireless headset that communicates with the cell phone from belt to ear provides longer runtimes than when placing the handset on the dining-room table while cooking in the kitchen. Although the quality of communication stays the same, the Bluetooth headset needs to work harder when placed farther away from the user.

The energy savings only apply when the wireless device is in the “on” position. When “off,” the load on the battery is very low and only provides power for housekeeping functions such as maintaining the clock and monitoring key commands. Housekeeping and self-discharge consume 5 to 10 percent of the available battery energy per month.

Laptop batteries fare badly in terms of life span. Laptops are demanding bosses that request a steady stream of power under poor working conditions, toiling in a warm climate. In addition, the battery is exposed to a high voltage when connected to the AC main. Warm temperature and full state-of-charge are the cause of short battery life in laptops, not cycling.

Modern laptops run cooler, so do tablets and smartphones that now share the laptop market. To provide reasonable runtimes on these devices, the battery size has more the doubled compared to a cell phone. Although reduced in energy consumption, a few power-hungry components remain and these are the prosessor, display and transmitter.

Following the advancements made in laptops, improving the specific energy of the batteries is being offset by added features. A survey conducted on laptops indicated that given the option of a larger size with added weight, most users settled for what was offered. This may also apply to smartphones and tablets. For better or worse, we learn to live with what we have.

Simple Guidelines to Prolong Lithium-ion Batteries


Last Updated 2015-04-29

*** Please Read Regarding Comments ***

Comments are intended for "commenting," an open discussion amongst site visitors. Battery University monitors the comments and understands the importance of expressing perspectives and opinions in a shared forum. However, all communication must be done with the use of appropriate language and the avoidance of spam and discrimination.

If you have a question, require further information, have a suggestion or would like to report an error, use the "contact us" form or email us at: [email protected]. While we make all efforts to answer your questions accurately, we cannot guarantee results. Neither can we take responsibility for any damages or injuries that may result as a consequence of the information provided. Please accept our advice as a free public support rather than an engineering or professional service.

Or Jump To A Different Article

Basics You Should Know
The Battery and You
Batteries as Power Source


On June 29, 2011 at 2:03pm
Niels-Erik Jensen wrote:

I have enjoyed reading your informations & instructions. Especially interesting (for me) was the information that batteries should not be charged to the full 4.2 volt especially if the battery is stored in a hot enclosure like e.g. an electric car. The battery should not be discharged to below 40% of full 4.2 V.

How many kWh is used to fully charge a 100 kWh battery that has been 100% discharged. There must be some loss as the battery gets very warm during charging

Discharging a fully charged 100 kWh battery to 50% will not deliver 50% to the electric motor as some heating of the battery occurs. How big is the loss

On July 15, 2011 at 11:33am
Dan Saint-Andre wrote:

I am technical enough to understand the voltage and current and charge details in your white (blue) paper.  However, I am at a loss to use this paper as a protocol for using my (1) laptop battery, and (2) mobile phone battery.

Just today, I bought and installed an new battery into my laptop. The papers told me that I should “... charge and discharge three to five times ... before full capacity ...” I interpret this to mean:
1. connect to power grid
2. wait for “full charge”
3. disconnect from the grid
4. use to “full discharge”
5. repeat 3-5 times

I have no idea what “full charge” and “full discharge” mean in practical operational terms. While my laptop has software that will report some numbers about the state of my battery, I will need to guess when things reach the above conditions.

Similarly, routine operation and use with the battery have details that remain obscure.
I did learn to remove the battery if running for long periods connected to the grid. It also seems that the battery should not be at “full charge” but at some lower level (80% ?) for storage during this interval.  How am I supposed to know that the battery is in the proper state before I remove it?

I know the answers, but “Why don’t laptop battery chargers and batteries have built-in condition indicators?” Similarly, “Why don’t laptop batteries have temperature indicators?”

Thanks for the article,
~~~ 0;-Dan

On July 26, 2011 at 12:24am
Sandeep wrote:

I have a laptop running on Li-Ion battery. What would be the energy wastage for the following cases running the same applications.
1. Laptop is running on a battery from which energy is being used. Once the battery level falls to 30%, it is charged until it reaches 100% and then discharge once again.
2. Laptop is continuously running on a charger but the battery is still in the laptop(100% attained).
Data Available - The application uses X Whr of energy
                  Charger converts 240V, 1.6A AC to 18.5V, 3.5A DC

On August 28, 2011 at 10:39am

My lithium 18650 2500 mah Thrustfire batteries take about 6 hours to attain full state of charge on a computerised programed charger. Is this normal?

On September 25, 2011 at 12:28am
Bob wrote:

This is kind of related to what Dan wrote.

I just purchased a smartphone and the instructions say to fully charge before first use.

1)  Is this really necessary?  Nothing I read on this site indicates that this is necessary or beneficial for a LIB.

In my excitement to play with the phone I skipped the charging and ran the phone until it shutoff by itself from a depleted battery.

2)  This is ok right?  I assume the battery and phone has safeguards to shut off before the battery is actually fully discharged.  As long as I charge it soon it should be ok, right?

USB vs wall charger.  Reading the text here mentions voltages and heat, etc, but nothing about current.  The text on my wall charger says it’s output is 1.0A at 4.8V.

3)  Will charging it through the USB port on my computer prolong my battery’s life?  It really takes a long time to charge on USB :( but if it’s going to help my battery in the long run, I’ll charge it through the USB port.

On September 25, 2011 at 12:30am
Bob wrote:

I forgot to mention that the battery is 1500mah.

Thank you.

On October 23, 2011 at 8:32am
mekong_nam wrote:

My cellphone, commtiva x1, with 1200mah original battery run for 24 hours after full-charged.I add 2 cell-batteries more, each cell 1200 mah Totally. my cellphone run with 3 batteries the same time, 3600 mah, and last for 96 hours after charged. Why does 3600 mah battery keep commtiva x1 cellphone run 96 hours in compare with 24 hours of 1200 mah battery? can some one help me explain?

On December 13, 2011 at 12:47pm
Guillaume wrote:


I don’t want to go in too much details so I’ll make my explanation brief. A battery does not respond to a linear model.

For instance, a 8AH battery with a given charge at 25°C might last 10 hours.

In the same conditions, a 16AH battery will give you more than 20 hours. (maybe 25 hours - it depends on many parameters)

On December 17, 2011 at 12:11am
Kyle Souza wrote:

Is it bad for the battery to be charging and using the device at the same time?  For example, is it best to have my cell phone off while it is charging?

On February 4, 2012 at 11:47pm
Nick wrote:

my laptop battery is old, so is my computer. I will charge my battery (li-ion 5400 MaH) to 100% then when the battery gets down to 80% it just dies. When I plug the computer back in, the battery is suddenly at 0%, then it charges to like 40% then jumps instantly to 100%. Is this normal? I plan to buy a new battery soon. How can
I avoid this from happening again? Please Respond! Thanks.

On April 9, 2012 at 4:58am
Chris B wrote:

In my experience the most important factor is not letting the battery get overheated, either by the device itself overheating or by leaving it somewhere hot like a car or windows in full sunlight. Doing that can kill the battery almost instantly.

On November 29, 2012 at 2:58am
Boris C. wrote:

What if a person lives in area with power outages and uses his laptop with lithium-ion battery as a backup method to warrant system from turning off in power outage situation?

There are 2 options but according to this article, both will shorten battery’s life because while performing short charges to battery and leaving it unplugged from mains while maintaining healthy charge between 40-50%, it will use charge cycles which I know are limited in lithium-ions. Another option would be to constantly keeping battery plugged to mains and although it will not perform many charge cycles, it will constantly keep battery under 100% which is not good for lithium-ion battery.

On November 9, 2013 at 5:19am
aamair wrote:

Hi guys
i am using a lenovo laptop
the problem is that the battery level suddenly drops from 20% to 6 %
can anyone tell me what might be the problem.
this laptop is 8 months old and i madly used it day and night on batteries and in plugged in state also

thank you

On November 9, 2013 at 5:31am
Boris wrote:

@aamair lenovo offers Energy Management software in downloads through their website where you can reset your battery’s gauge. That’s what I did when my battery dropped suddenly from 80% to 10% and it fixed the problem.

On March 31, 2015 at 12:13am
Michal Bittsansky wrote:

I believe it is not true that the phone broadcasts all the time to the tower. According to my observations and measurements, the phone only registers at the tower, so that the tower “knows” that the phone is within its reach. Then, the phone only CHECKS the tower signal and it is the tower, that broadcasts permanently. Only when the phone realizes that the tower signal decreases, it solves the situation by checking other available towers. I believe that checking the tower transmission is much less costly in terms of energy then broadcasting to the tower.

On September 21, 2015 at 3:16pm
Daniel Shamailov wrote:

My friend is crazy with his phones and one thing he always does is wait till the phone reaches 10% then charges it to 100%, unplugs it, and repeats the cycle. He says that plugging it in above 10% is bad. Is he right or wrong?