[andyukguy]

Hi,

Does it make more sense for me to leave my iPhone connected to 3G or to WiFi when at home if I want to maximise battery life? I have:

- An iPhone 3GS running iOS 4.3.1

- A 3G signal that fluctuates between -95 and -116dB

- Push notifications on

- 6 IMAP email accounts being checked every 15 minutes

Thanks.

[3GScottishUser]

Any additional transmission and reception on any handset will drain the battery life. Wi-Fi and Bluetooth are best switched off when not needed as they can drain a lot of power.

If data allowances are not an issue I would leave the WiFi and Bluetooth off and let the mobile network push e-mail notifications to the phone whilst you are at home. You can always switch the WiFi on to receive the message bodies and attachments if you receive anything of interest. Then again if you are at home why not just plug in the charger!

[Hands0n]

I leave WiFi and 3G permanently on on my iPhone (always have) allowing it to find the best signal for the location. Basically, I'm just too darned lazy to be fiddling with the settings constantly.

I have four eMail accounts on the go, three push and one pull, Twitter and Facebook with push notifications.

Battery life for me is a full working day easily. On a weekend, where I use it more than during the week, I will often get down to about 32% battery charge left. My personal regime for all my smartphones is to charge them up overnight without fail, they go on charge just before I retire for the night. Sometimes I will take an "opportunity charge" from a source such as in the car or in the lounge where I have a spare USB power source available.

[andyukguy]

Thanks for the replies guys, I was hoping someone might have more technical knowledge on whether in my use case 3G or WiFi would provide me with the greater battery life. I guess I could just do a test myself, but I like knowing the technical side of things e.g. 3G is better and will give you more battery life in this situation due to x, y and z...!

[Hands0n]

It is unlikely that there is much difference between the battery usage between 3G and WiFi. What does hurt battery life is if your handset is set for 3G and you are in a marginal area that causes the handset to flip from 3G to 2G and back again. While in 2G the handset is "hunting" for a 3G signal and therefore will consume much more battery power. The early days of 3G were plagued by this where the mobile operators roll-out of 3G transmitters was sparse. These days the situation is less likely, although all networks do in fact have areas of little or no coverage of 3G.

The smarter smartphone OS will not attempt to use 3G while they are attached to WiFi - with the mobile network only being used for voice and SMS/MMS while on WiFi. This has the benefit of containing the usage - it is not like in the early days where the WiFi and 3G were belting away at the same time. The handset will make smart use of the radios, thereby saving battery life.

Bluetooth and AGPS (when active) can be heavy battery users, and so should normally be left off or in a state whereby they are only activated on demand. Both Android and iOS do this with AGPS but not Bluetooth.

In all cases, the radios go into a hibernate mode when the handset goes into standby. The 3G/2G radio will maintain "presence" with the mobile network, that is like a keep-alive, that is repeated periodically. Otherwise the network thinks you've gone off-net and de-registers you at that time until it sees you re-register again. So there is a whole lot of optimising going on in a current-day smartphone OS. Lessons have been learned from the past experience.

So, between 3G and WiFi I do not believe there is anything much in it between them. The real kicker for battery life is more about how much on-line use you make of the device, how long you keep the radio/s active for.

Perhaps this will help some. My Nexus S since being unplugged this morning has been running 14h 55m 42s on battery. In that time it's battery use utility says the following usage has been made of the battery:-
Display 41%
Mobile standby 31%
Phone idle 13%
Android OS 5%
Andrid system 5%
Screenshot 2% (an app I used today)
Gallery 2%

[Ben]

Hi andyukguy!

Sorry I'm a bit late to this one.

From Apple:
Internet use
up to 5 hours on 3G
up to 9 hours on Wi-Fi

My feeling is that you're going to get far better battery life with WiFi on given all that regular data access you're doing. If you have good 2G signal at home you could, if you wanted, disable 3G entirely and just use WiFi + 2G and that should yield optimal battery life, but to be honest unless your 3G coverage is very weak or your phone switches 2G/3G a lot I don't think it'll make much difference.

I always, always observe better battery life when I leave WiFi enabled if I can connect to a WiFi hotspot. Power management in iOS is pretty good.

[DBMandrake]

If you hardly ever use data - eg when you're using the phone you're almost exclusively doing things that don't download data from the internet, you'll notice a slight increase in battery life by turning Wifi off, as Wifi has to transmit a short burst periodically (every 10 seconds or so) whenever it's connected, regardless of whether there is data to be sent.

However if you actually use data to any significant degree you'll get much better battery life by using Wifi than 3G. 3G has almost no standby overhead (after all it's on all the time waiting for calls) but when you actually use data 3G uses a lot more power than Wifi.

If I do a lot of downloading on 3G the phone gets quite warm, if I download the same data on Wifi it doesn't. I think that says it all :)

In the OP's use case I would say definitely leave Wifi on at home.

[3GScottishUser]

Have I missed something here?

The OP will be using the handset at home so to repeat the obvious and take advantage of all the facilities, plug it into the charger.

Simples!

[andyukguy]

"At home" was merely an example to show the phone wouldn't be moving between signal strengths. The question was definitely meant to be a more technical discussion on which radio would give me the better battery life in my use case. I will leave WiFi enabled methinks as that is the consensus :)