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turtle777 · Aug 5, 2008, 06:41 PM

I finally realized what makes my iPhone's battery drain so badly. WiFi.

In one office with WiFi, my battery will be at 20% sometime in the afternoon, in the other office, w/o WiFi, I'm at 85% battery in the evening. (Both running on EDGE, not 3G)

Why is the power management for WiFi so bad ?

-t

ghporter · Aug 5, 2008, 09:37 PM

It could be that in some places it takes more radio power to contact the access point than in others. WiFi allows the transmitter to adjust its power level to maintain a connection, and if you're in some place with poorer coverage, you might just be using more power to connect to a more distant tower. This is much like simple cell phone connections, where the phone's transmitter changes power as directed by the cell site, but with WiFi it's done by the mobile device itself.

This is just my opinion, since I don't have an iPhone, let alone experience like you're reporting, but I'd be very interested to see what sort of signal strength you have in places where your battery runs down faster.

turtle777 · Aug 6, 2008, 12:16 AM

Yes, that might explain parts of it. I would need to monitor if the WiFi signal strengths shows a observable impact on the battery staying power.

Still, the battery management seems to have issues. My battery is getting strained on WiFi, even if I'm not using it at all. You'd think it'll go to some sort of sleep mode with minimal power draw

-t

Simon · Aug 6, 2008, 02:59 AM

In terms of battery life it's a good idea to turn off "Ask to Join Networks".

turtle777 · Aug 6, 2008, 09:15 AM

Originally Posted by Simon

In terms of battery life it's a good idea to turn off "Ask to Join Networks".

How does this in particular use up a lot of battery ?

When I'm in areas w/o WiFi (but "Ask to Join Networks" turned on), battery life is still MUCH better than when I'm in areas with one WiFi network that doesn't change.

What' I'm trying to say: Does the energy consumption depend on changing WiFi networks, the more change, the more consumption ?

-t

Simon · Aug 6, 2008, 10:13 AM

If the setting is turned on your iPhone is constantly polling for networks. If it's turned off, your iPhone will only checks once (when it's activated) to see if one of the "known networks" is available.

ghporter · Aug 6, 2008, 10:27 AM

I was going to draw the distinction between "off" and "not using it" myself. If WiFi is OFF, it won't use ANY power. If you're not using it, why not just turn it off until you need it?

turtle777 · Aug 6, 2008, 10:35 AM

Originally Posted by ghporter

I was going to draw the distinction between "off" and "not using it" myself. If WiFi is OFF, it won't use ANY power. If you're not using it, why not just turn it off until you need it?

But I found that this is NOT necessary. When I'm in a location w/o WiFi, even with WiFi and "Ask to Join Networks" ON, it still doesn't draw a lot of extra energy.

The problem is when being connected to a WiFi network, it sucks energy, not matter if you actually transmit data or not.

-t

Don Pickett · Aug 6, 2008, 10:41 AM

I've found that if my Touch can almost connect to a wireless point, it kills the battery. In other words, I think it's the polling and connecting which uses battery.

Where I'm currently working there's a wireless network which is just out of range: the Touch can get an IP address and a subnet mask, but not a router IP or DNS list. So, it sits there, polling and polling that point, trying to connect, and it kills the battery. Because of this I just turn te WiFi off when I'm in the office.

turtle777 · Aug 6, 2008, 10:44 AM

Originally Posted by Don Pickett

I've found that if my Touch can almost connect to a wireless point, it kills the battery. In other words, I think it's the polling and connecting which uses battery.

Where I'm currently working there's a wireless network which is just out of range: the Touch can get an IP address and a subnet mask, but not a router IP or DNS list. So, it sits there, polling and polling that point, trying to connect, and it kills the battery. Because of this I just turn te WiFi off when I'm in the office.

But it shouldn't do that when it's fully connected to a WLAN network, right ?

While connected to a WLAN network, why would the iPhone with "Ask to Join Networks" turned on still try to connect to other networks ? Shouldn't it only try to find other networks if no current network is active and in use ?

-t

Don Pickett · Aug 6, 2008, 10:50 AM

Originally Posted by turtle777

But it shouldn't do that when it's fully connected to a WLAN network, right ?

While connected to a WLAN network, why would the iPhone with "Ask to Join Networks" turned on still try to connect to other networks ? Shouldn't it only try to find other networks if no current network is active and in use ?

-t

See my post: I have a Touch and not an iPhone. However, I think the battery drain issues are the same.

ghporter · Aug 6, 2008, 05:07 PM

Even if you're not "sending data", you ARE sending packets. Empty packets. That's how the client stays connected to the host. So if you aren't actively using the connection, if it's there, it's using power.

turtle777 · Aug 6, 2008, 05:10 PM

Originally Posted by Don Pickett

See my post: I have a Touch and not an iPhone. However, I think the battery drain issues are the same.

That's what I assumed.

Except if there is a different battery management software in the iPhone. But I would think that's part of the firmware, and would be updated in both devices.

-t

turtle777 · Aug 6, 2008, 05:48 PM

Originally Posted by ghporter

Even if you're not "sending data", you ARE sending packets. Empty packets. That's how the client stays connected to the host. So if you aren't actively using the connection, if it's there, it's using power.

I know, but wouldn't you expect that there is some sort of smart way to make a difference between WiFi sending zero packets and WiFi under full load ?

I just wouldn't expect 12 hours of zero packets to drain the battery completely...

-t

Randman · Aug 6, 2008, 06:01 PM

Go into Airplane mode one or two days and compare battery life.

ghporter · Aug 6, 2008, 07:12 PM

Originally Posted by turtle777

I know, but wouldn't you expect that there is some sort of smart way to make a difference between WiFi sending zero packets and WiFi under full load ?

I just wouldn't expect 12 hours of zero packets to drain the battery completely...

-t

"Zero packets" are just that: valid packets with their data fields filled with zeros. They are still being sent...

turtle777 · Aug 6, 2008, 08:25 PM

Originally Posted by ghporter

"Zero packets" are just that: valid packets with their data fields filled with zeros. They are still being sent...

I understand that. But the question is: HOW OFTEN are those zero packets sent ?
Is there a need for sending those every 30 seconds or so ?

That's where intelligent power management comes into play. (or at least should, for that matter).

-t

ghporter · Aug 6, 2008, 09:20 PM

If it works with broad-area WiFi the way it does with WLAN WiFi, it's pretty much continuous. Not every 30 seconds, but all the time.

And the phone doesn't know what you have in mind, so it can't be "intelligent" in managing power without being a royal pain when you want to surf and it has to reconnect.

Simon · Aug 7, 2008, 02:38 AM

That's the point. People want networks to be discovered as soon as possible and not after 5 minutes. So packets have to be sent at a higher rate. There is no "intelligent" management that can be added here to save battery power. The only thing you can do is turn searching off or turn WiFi off altogether.

Leighgion · Aug 12, 2008, 03:16 AM

Laptops run down faster with wifi on too. They just have much larger batteries than iPhones and we're used to considering laptop run time as including wifi load if we can possibly get it.