Very often I hear the statement – don’t leave your phone registered to the UMTS (3G) or GPRS (2G) network, as this will decrease its battery life and you’ll need to charge it more often.
Today I decided to bust this myth and also to compare if UMTS (3G) uses more battery power than the slower GPRS (2G) transfer standard.
The theoretical speeds of the GSM standards in question follow:
– GPRS (2G) – up to 114 kbps (~14 Kbytes/s)
– UMTS (3G) – up to 2 Mbps (~250 Kbytes/s)
The following was tested with a Nokia 5800 XpressMusic via a Bluetooth connection to a computer. The Bluetooth connection itself uses some power but my measurements show that its usage is about 0.15W, so we will consider it negligible for our benchmarks.
The power usage was measured using Nokia Energy Profiler.
So here are the end results about power usage in different scenarios:
- 0.40W – no connections at all.
- 0.40W – no Bluetooth connection, just registered to 2G or 3G network.
- 0.52W – Bluetooth and 2G or 3G connections established, but connections are idle.
- 1.27W – 8 Kbytes/s (64 kbps) download via 2G.
- 1.69W – 65 Kbytes/s (520 kbps) download via 3G.
- 1.73W – 120 Kbytes/s (960 kbps) download via 3G directly from mobile phone, no Bluetooth. If we add the Bluetooth power usage, this would sum to up to 1.90W.
The myth is busted: Leaving your phone registered to the 2G or 3G network shouldn’t drain up your battery faster, if you make no traffic to the 2G or 3G network.
Update: Maybe I spoke too early. As “varnav” commented below, the 3G mode may make your talk time 2+ times less. At least that’s what the technical specifications of iPhone show. I haven’t tested this but I doubt it that Apple haven’t, so they are probably right, at least for their iPhone models. 🙂
Conclusion: You should use 3G if you are about to make data transfers and probably it is better to turn it off after that. Nokia 5800 has an option to enable the 2G/3G data connection only when data is about to be transferred, and this is what I currently use as settings.
Let’s analyze if 2G or 3G uses more power if you start making data transfers. First impression is that 3G uses more power. However its transfer speed is much greater, so the overall Watts usage for the same downloaded size will be smaller, which makes 3G more efficient and thus less power consuming in practice.
Here is an example to illustrate the above statement. Let’s assume that we want to download 1000 Kbytes:
- 2G: 1000 Kbytes at download speed 8 Kbytes/s will take 125 seconds. At the power usage of 1.27W this will take about 159 Watts-seconds (125 seconds * 1.27 Watts).
- 3G: 1000 Kbytes at download speed 65 Kbytes/s will take 15 seconds. At the power usage of 1.69W this will take 26 Watts-seconds (15 seconds * 1.69 Watts).
Therefore, using 3G the consumption has decreased to 16.3%! Yes, in this case 3G would use six times less energy from the phone battery, if we downloaded the same amount of data using 2G, at maximum speeds.
One interesting power usage pattern by 3G is that when you stop the data transfer, the power usage doesn’t drop immediately to the full idle state. Instead, about 0.80W is drained for about 30 seconds, and then the connection is put in total idle state. Review the power usage images below, in order to get a better idea of what I mean. Even if we add up these 24 Watts-seconds (30 seconds * 0.80 Watts) to the above calculations, 3G would still use 318% less energy.
June 1, 2010 at 5:44 am
Hmm, so there’s no power usage difference between having the phone idle on 2G or 3G?
People keep suggesting to stay on 2G until you need to browse the web/etc then switch to 3G.. but im guessing this is just a big myth?
June 1, 2010 at 9:27 am
I don’t know how much power goes for the initial 2G/3G connection establishment and how often it’s done, but as far as leaving your phone idle without data transfer on 2G/3G, this seems like a myth. 🙂 At least on my Nokia 5800.
June 27, 2010 at 5:58 pm
Yes, 3G drains more power compared to 2G only if data is transferred.
But, in areas with poor 3G coverage, constant 2G/3G switching will drain power, so even if cellphone lies on a table it can eat up it’s battery in one night.
And, worse, it makes 3G a bad thing when it is about to use the main feature of cellphone – talk, draining battery 2+ times faster than in GSM network.
So, if you don’t surf more than you talk it’s better to keep 3G mode deactivated.
June 27, 2010 at 6:02 pm
As well, many people say that phone with 3G mode on will drain more power when there is no 3G network – because it will have to actively scan for it.
So, try to test power consumption somewhere where there is no 3G coverage.
There was the same problem with no-network-battery-drain in early days of GSM.
August 18, 2010 at 4:34 pm
2G GPRS is best for calling while 3G is for data:like 1st gear & top gear!However,future of 3G is unpredictable at present!:syedali
August 23, 2010 at 7:56 pm
September 3, 2010 at 7:09 pm
did you do this will moving? or were you stationary????
September 3, 2010 at 7:17 pm
Stationary. The signal level meter on my phone shows maximum reception.
November 10, 2010 at 10:52 am
Interesting article, however Watts-seconds is a strange expression:
Watt = Joule / seconds, so
‘Watts-seconds’ = Joule / seconds * seconds = Joule
November 10, 2010 at 11:19 am
🙂 Watts-seconds refers to the energy used for the communication, and yes, it is measured in Joule in physics. Watts-seconds is the same as Watts-hours, which is much more commonly used. The Watt->Confusion of watts, watt-hours, and watts per hour Wikipedia article sheds some more light on this topic.
March 17, 2012 at 1:03 am
It’s true power is work /time simple physics
April 27, 2011 at 10:32 am
what about power consumption figure if we do voice calling for an hour on 2G and 3G network?
April 27, 2011 at 12:29 pm
I haven’t tested this but this is a good idea. If you manage to test it, share the results and I’ll publish them. Or you publish them, and I’ll link to your page.
May 28, 2011 at 1:15 am
What about this: i use some gadgets for random chat rooms, weather reports, clock sync, mail checks (notifications only)… so basically just a few kb every few seconds or minutes where transfer speed is “irrelevant” from practical point of view.
According to this research, 2G only would spend less or?
May 28, 2011 at 2:31 pm
3G is more efficient for data transfers, even for small ones. But there are 2 caveats:
* some report that using 3G and talking could use more battery power
* on my phone, after the 3G transfer, for 30 seconds the line is idle but consuming power
So you need to benchmark for your particular transfer, because if it’s really small and not so often, you may be better with 2G.
August 8, 2011 at 5:02 pm
In my opinion, this is what would optimize the battery usage in a regular smartphone user:
* while having your phone locked, use only 2g connection. Generally you only receive small messages (i.e. whatsapp popups) while you’re not using your phone
* switch to 3g connection as soon as you unlock your device. This way you can use the max speed while surfing the web or whatever.
What do you think about this? I recently jailbroke my iPhone and there’s a tweak that allows you to immediately switch your connection type when you lock/unlock your phone and I thought this would be the perfect combination, but I’d be glad to hear your word about it.
August 9, 2011 at 10:11 am
That’s a great idea! … that needs testing 🙂 I would do it on my phone too if I could. A friend of mine yesterday told me that the battery of his Android phone lasts much longer in 2G. It’s worth mentioning that my Nokia, for example, cannot seamlessly switch between 3G and 2G — it disconnects from the network for a few seconds, and one may miss an important call.
I’d be glad if you try what you suggest for a few weeks and then share your experience.
October 11, 2011 at 2:34 am
“Therefore, using 3G we would spend 611% less power!” This would mean if the consumption was 159J (joule, or W×s) now it becomes –812.5J. What you should have written is that the consumption has decreased to 16.3% (or a 6th) or it has been reduced of 83.6%.
Please, forgive this engineer 😉
October 13, 2011 at 10:11 am
Priceless comment, thanks for the correction.
October 11, 2011 at 10:53 am
I always have my phone in my pocket, and since this is causing bad 3G coverage, with following switching from 2G to 3G and back then I moves around, I always switch to 2G then phone is un used.
One of the worst thing to battery consumption is then the phone tries to update my emails while connected to a 3G net with bad coverage.
January 25, 2012 at 3:00 pm
wonderful comments by the engineers. i think my battery (iPhone 3GS) lasts a little bit longer on the GSM network (at&t). I don’t use 3g and I don’t use the phone for listening to music or watching vids or anything that requires “data”. If I play with it for “data” i do it here in the house on WiFi and not at&t’s network for which I would pay.
July 24, 2012 at 6:23 pm
Your watt mathematical usage is factored wrong… Since my Phone has more than 2 watthours or 2000 miliamiamps ( divided by a 1000 to equal actual whole watts) times the 3.7 volts=7.4 watts… by your calculation my battery will be dead in a a few microseconds…. nice attempt… real mathemematics… since watts are measure in hours… how many seconds r n an hour? 60 seconds are in a minute times 60 minutes to equal and hour… thus with this factor of 3600 if I divide your calculations I still fall wrong by sensly knowing 2 hours connected = dead battery…. thus I believe you’ve forgotten to divide by 60… either seconds or minutes was forgotten…. wait still 2 watts doesn’t even sound correct.. there’s many factors to consider in consumption as uve attempted to discover and reveal it
July 25, 2012 at 12:19 pm
I see nothing wrong in the calculations. The Watt usage data comes from the “Nokia Energy Profiler” application which probably uses the phone internal power measurement systems. So data should be more or less correct.
If your battery is 2000 mAh (that is 2000 milliamps-hours or 2 Amps-hours) at 3.7 volts, you would have 7.4 Wh (Watt-hours) energy in the battery (theoretically; a bit less in practice, I guess).
Using some of the measurements above:
– With just the display working at 0.40W, you can use the phone for 7.4 Wh / 0.4W = 18.5 hours. Seems fair to me.
– With a full speed 3G download at 1.73W, you can use the phone for 7.4 Wh / 1.73W = 4.28 hours. Which also seems correct.