When I got my iPhone 4 I was impressed with the battery life (for a smartphone). I could easily last 48 hours even with regular usage (and much longer that on lower usage).

Even running Skype in the background it only burned though around 4-5% an hour.

However, just before Christmas, around the time that I installed iOS 4.2.1 it changed. It suddenly started burning 4-5% an hour even when idle, even if it had just been rebooted and no apps had been run.

I tried fiddling with various things, but it kept doing it. I assumed it was:

- a problem with the hardware (which would get sorted out when I got round to swapping the hardware due to the failing button)
- a problem with iOS 4.2.1 (which might get sorted in an update)
- something about my setup or one of my many many apps (though couldn't quite see how as the apps weren't running after a reboot)

I got the hardware swapped last week and the new phone kept draining at 4-5% per hour. So I was then fairly sure it wasn't the hardware.

I spent a couple of days working away from home this week and it magically seemed to go back to sipping 2% and hour (even though it was having to use 3G rather than wifi most of the time).

So when I got home I had a thought about anything I had changed at home around the same time. I remembered that I had been experimenting with setting up a second wifi network on the wifi on my router. I had connected the iPhone to this second network to test it.

The two networks are identical apart from the ssid and key. But it looks like for some reason being connected to that second network was draining the battery.

I switched it back to the old wifi network yesterday and battery life seems to be back to <2% hour. All very odd and the last thing I expected to be causing the problem.

"It just works", some times...

Did you turn off SSID beacons?

Is that the same as hiding the SSID or something else ?

Neither SSIDs are hidden.

Yeah. Its not really turning it off. Its just filling the SSID field in the beacon with nulls.

Your laptop/phone has to actively probe to work out what these (not so) "hidden" networks actually are. It'd be asking if that hidden network is actually <blah> SSID at which point the AP will respond and say yes or just ignore it if it isn't.

If somebody has something which can see these raw WiFi frames then they'll be able to tell what SSIDs you've got configured on your device.

Is this second network the only network configured in your iPhone?

The iPhone has many wifi networks configured on it.

It is configured for both the wifi networks on my local router.

If its set to both then wouldn't it switch between them a lot?

No. As far as I can tell, when presented with a list of wifi networks that it knows about, it connects to the last one you selected it to connect to.

Only other thing I can think of is that your router is capable of multiple SSIDs but is only capable of using a single BSSID and the iPhone doesn't like that.

What router/AP do you have?

Vigor 2820

Andy, I know your issue wasn't app related, but do post back if you notice an unusual battery drain with apps. I have found a number of other bad citizens since posting about the subject in the other thread.

Bria, a voip app, will eat the full battery in about 6 hours if I don't force quit it. In other words, I can go back to the spring board, sleep the phone and 6 hours later I'll be lucky to have a single pixel on the battery meter.

A couple of clock apps also consumer crazy amounts of battery, including Awaken which I've most recently tried. It seems to suck more than its share while running with the phone asleep or even while in the background.

IMO, Apple should be putting more millions into research of battery tech/chemistries. I know it's not necessarily a problem that can instantly be solved with money, but I think a cool billion over a couple of years should yield some fruit. Personally, I'm looking for a 10x increase in battery capacity. IMO, it's currently the biggest issue holding back portable devices at the moment. Processing speed, memory and storage are all reasonable right now.

Storage isn't there yet for me, I'll be happy when the cram 64GB into an iPhone.

I'd love more storage too, but IMO, that's more a cost/marketing restriction at this time rather than a technical hurdle, that's why I didn't mention it.

I'd actually prefer skipping 64GB and going directly to 128GB at a minimum. My locally stored copy of WIkipedia alone takes up close to 6GB without images. Space goes quickly when you start to add apps/games that eat anywhere from 500MB to 1GB. Then movies take up a lot of space, in the end not leaving a tremendous amount of room for music.

For me, in terms of wider battery issues, it's recharge times that are the real blocker right now.

You're right, they do go hand in hand. I'd really hate to see a 10x increase in charge time along with the 10x increase in capacity, so much shorter charge times is also something that needs to be worked out. In fact, if it doesn't, it would likely hold back the capacity. You can't afford to have a phone down all day sitting charging just so you can have an extra long run time later on.

Can you imagine how beefy the chargers would need to be to have 10x capacity batteries and keep the charge times as they are now

It all depends on what the ratio of fairy dust to unicorn tears is in the battery chemistry.

I think it depends on Mr Ohm.

Wasn't there some battery chemistry a couple years back that was supposed to be super fast charging? It never appeared even though it was the Next Big Thing (tm)

[edit]Found it. 20 seconds instead of 6 minutes and it doesn't lose capacity if you just leave it there.[/edit]

Ask Steve (or whatever it is thats temporarily running Apple) for a fuel cell powered iPhone.

Looks like it is shipping in a number of products, just not widespread yet.

http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery#Usage

I'm not seeing this behavior on my iPad. I've always manually pointed it to my 5ghz network, and it reverts all the time to my 2.4ghz network. I've finally just told it to forget the 2.4ghz network. Though, my issue might be different, as I'm guessing it picks up on the 2.4ghz one quicker when I'm walking towards my apartment, and just sticks on that even though it later sees the 5ghz network.

Interesting. I can see people who use RC devices as a good market for this.

I wonder if its the special fast charging version of the battery though as mentioned in the article. The 6 minute charge is for an "untreated sample" of Lithium Iron Phosphate and the 20 second charge is for whatever they did extra that makes it capable of fast charging.

A123 batteries are popular with RCers already. But they are bigger and heavier batteries so only appropraite for large planes or surface vehicles. Then can be charged at more than 1C rate though- something LiPos batteries can't do safely. Also A123 batteries are less likely to explode and set your house on fire- which is always good. LiPo batteries are one of the reasons I never got very far into RC planes (besides I crashed all the time) couldn't justify burning my house down for a hobby.

Ouch, you'd need a big charger and a damn thick cable....

5.25Wh in 6 minutes = 52.5 watts (without charger losses), over 10A current at 5V, so that'd be looking like a (UK) electric kettle's cable....

5.25Wh in 20 seconds = 945 watts, again without charger losses, or 189A current at 5V. Bus-bars? Welder?

Yeah, you can drop the amps by putting a switchmode charger in the device itself, but then you'll end up with having to put a whole AC brick in there along with the size and mandatory insulation gaps required for high voltage....

You could always charge them at a nice safe 0.7C, and have plenty of spares?

To me, that just screams lack of dedication The first question I had when I heard about the faster recharge rate was 'How many laptops are going to explode because of batteries now'?

You mean spare houses

Yes I'm sure you can charge LiPos safely- but apparently sending them nosediving into the ground also makes them more likely to explode. Somehow that happened a lot to the batteries strapped to my RC planes.

5 years ago (five... Can't believe so much time ago) I converted my 1/8 buggy to electic, and I was using super expensive, at the time, LiPo batteries. They've been sitting there in the buggy since then, on a shelf, as I had never time to devote to run the buggy again. I wonder if I should take the LiPos out and dispose them? Do you think they're still good? Actually, would anyone here make any good usage of those (I should be able to provide specs if needed)?

Doubt they'll be still good. Lithium batteries start to degrade the minute you've manufactured them. If they're not in proper storage conditions (temperature and charge level) as well then the degradation is going to happen even faster.

One of my phones from a few years back had no cover over the battery pack. The back of the LiPo battery case acted as the "cover" so it was fairly exposed. One day I noticed that I had my keys in the same pocket and that I must have sat down with the keys pushing against the phone. There was a dent on one side of the battery pack and a little bump on the other side where it must have deformed every layer inside the battery. I was lucky that it didn't explode or burst into flames in my pocket!

It's surprising how much abuse modern LiPos can take, actually. I managed to fly one into the ground a few years ago, which mushroomed to the point it was nearly t-shaped on one end, and it still worked fine. I didn't actually trust it anymore, of course, but it did work.

I've got a couple of batteries that took on a distinct curved shape after some heavy use, and are still ok. The really key indicator is if the casing begins to swell. A little swelling after long use it unavoidable, but if rectilinear pack becomes a cylindrical one, get rid of it.

pca