This is a strange one really. Like most smartphones, my 3GS doesn't have an amazing battery life. However, I've become accustomed to what I can expect. For example, yesterday on the train I used it pretty much constantly for two hours (texts, internet, GPS, and various apps using push notifications) and it sapped around 50% of the battery. That's fine. I later charged it.

When I went to bed at 2am, I had 40% of my battery remaining. As usual, I switched off wi-fi, quit any running apps (not that they are running for all intents and purposes anyway, but you know what I mean) and set the alarm.

The alarm, which was set for 8am, never went off, because the battery was dead. So in six hours of doing nothing, it lost 40%. I realise it was still checking for email etc, but that doesn't normally use anything like that amount of battery. In fact, usually if I just leave it for a few hours and do nothing, the battery hardly drains at all.

So - what's causing this? It's a bit of a mystery. It has drained more than usual overnight in the past, but never 40%! I live in a poor signal area so it's frequently searching for a signal - could that be having an effect?

Yes, a poor signal will have an effect. If it's losing a signal often then scanning for another one this can drain the battery a lot.

If your worried about this happening again and not too bothered about having a signal while in bed perhaps switch it to flight mode which should help, but will of course mean you can't receive texts or calls.

There's been a lot in other forums about battery drain rceently. I was told that Ping uses up a lot of power. Go into settings-general-restrictions (set a code if you've not done so before) and turn off Ping if you don't use it. I'm convinced my battery is lasting longer today than yesterday when I switched it off.

Just change the battery if it's faulty.

You can do a simple thing like that on an iphone cant you?

Yip I changed the battery on my iPhone 3G when it started to get old.

Unlikely the battery is at fault here though, more than likely a software issue or the battery needing run flat and fully charged.

I tried to make it clear that this isn't a simple case of the battery generally running down quickly. For example, I took it off the charger at 3.30pm at 100%. Since then, I've made a few phone calls, sent texts, used Facebook, spent an hour in the gym listening to music, and had all the usual push notifications on. The battery is now on 61%. That's why I was confused about it losing 40% in six hours when it was doing nothing.

It must be to do with it constantly dropping signal overnight. My bedroom is a notorious dead zone (in terms of phone signal ) so it's probably spending all night searching for a signal, acquiring it for a short time, then losing it again.

Since I have it on silent overnight anyway, I made as well just put it on flight mode from now on.

Might be worth trying a replacement battery,

Essentially what I'm saying is that the battery runs down overnight when it's in my bedroom doing nothing than it does at other times. It's not done it before to this extent, but it has done it before. If I'm at work and don't touch it all day, it loses hardly any battery at all.

I tend to think it isn't a general problem with the battery, as it only occurs in the situation I've described.

Strange I have an iPhone 3G on orange which until recently would get and lose a signal all the time as my orange signal sucks and would never lose even close to 40% battery at night.

Might be worth testing the battery by placing the phone in airplane mode over night just to see how much the battery still drains. Should hardly be anything at all, about 2 or 3%.

I will put it in flight mode tonight (still can't bear to call it airplane mode, too American!!) and see what happens.

I wouldnt have expected it to lose such a large chunk of battery life from a poor signal either, to be honest. But I haven't noticed battery drain during any other time.

Just plug it in overnight. That's where I do my charging, with a quick top up before I set off for home if needs be

Do you use a Twitter app? I noticed mine was leaving location services on which is possibly a huge battery drain. I turned them off and it's a bit better but still a noticeable difference compared to before the latest firmware update.

I use the official Twitter app.

Well, I put it in flight mode at 2am. It had 68% battery. Then, at 8.30am, after my alarm went off, I noticed that the battery was on 62%. I wouldn't have expected it to lose 6%, but at least it didn't drain down to nothing!

There you go, just slide the case off and change the battery.

:yawn:

Never know, it might be a feature on the new one..

'We've now invented changable batteries'.. We call it.. Batterytime©'

Those with battery issues since iOS 4.3 might want to try download iOS 4.3.1 - although its currently unconfirmed whether this fixes the problem.

edit: What has been mentioned is that this is also believed to patch a security vulnerability that hackers recently demonstrated at an annual hacking competition.

I've noticed an overnight draining issue too on 3GS. Go to bed with 100% charge, get up with varying degrees of less than that. As much as 10%. Before 4.3, it'd be more like 1 or 2%.

Downloading 4.3.1 now. We shall see what % I have tomorrow morn.

Well of course your phone will lose battery whilst it's switched on.

I charge mine every night.

Yes, I know. But the issue is I'm sure it's losing more now than it did before 4.3.

Batteries deteriorate (albeit very slowly) with each discharge/charge cycle though.

you dont need to keep turning wifi on and off anyway, as when the iphone is sleeping, its off anyway

On the iphone4 you just undo screws on the bottom then slide off the back cover

Are you running any GPS apps as they constantly search for a signal and this can eally play havoc with your battery.

I found Google maps was a very bad battery drain