FILE PHOTO: A customer holds the iPhone X during the global launch of the new Apple product in central Sydney
INTERNATIONAL - If you haven't updated your iPhone to iOS 11.4 yet, you may want to hold off a bit longer.

Frustrated Apple users are complaining that the software update is killing their batteries.  One angry user wrote on Reddit that it caused their battery to drain up to 25% faster, while others say they are constantly having to charge their phone.  

Apple has not yet revealed what is causing the problem or how to fix it.   However, some users suggest that the issue may be with the background app refresh feature.

This lets your apps run periodically in the background so that they can update their contents, even when you're not using your phone.  To turn off the feature, launch the Settings app from your Home screen and select General. Then switch Background Refresh to 'off'.

The iOS 11.4 update, released globally on May 29, gives iPhones the ability to store messages in the iCloud. It also includes improvements to the controls for Apple's new HomePod smart speaker and multi-room audio. 

FILE PHOTO: WhatsApp and Facebook messenger icons are seen on an iPhone in Manchester , Britain.
However, battery drainage appears to also be a feature affecting devices across the Apple range.  'My iPhone 6 was working perfectly fine until I updated to iOS 11.4 and ever since I did that my battery is draining rapidly even without me using it at all,' said one disgruntled user in a consumer forum.

'I used to go a full day without charging it [and] now it may last half a day. I am just wondering if something got turned on with this new update that I have to turn off to save battery life.'   'It is just weird I have not done anything other than update the iOS and now this happening.' 

Twitter users also spoke about their plight, urging others not to update and asking if others had fallen foul of the same issue.  Bharath Chamarajanagara tweeted: 'If someone hasn't done it yet, then please don't update to iOS 11.4. The battery drain is serious and terrible. Please wait for a fix before upgrading'.  

However, not everyone appears to be affected by the issue.  'My iPad Air 2 has no problems with the battery. I left it at 99 and woke up with 98,' said one Apple fan.

Another wrote: 'Odd. My [iPhone] 7 Plus seems to be performing better with no noticeable battery draining.  'I'm typically on my phone all day from 9am to about 10pm with small charges from my car in between.' 

Apple has not yet responded to a request for comment.   Forbes points out that affected users are primarily reporting that the issue happens at home.

This suggest that background synchronisation services could be to blame.  These primarily work when your phone is idle and connected to a home WiFi network. 

Some users suggest turning off WiFi to stop the battery from draining as quickly.  This is the latest in a series of battery issues Apple users have faced. 

Last month it was revealed that if you paid for an iPhone battery replacement from Apple last year, you could be due a £54 ($50) refund.  Apple has been charging a discounted £25 ($29) for out-of-warranty replacement batteries for the iPhone 6 and newer models since December. 

It dropped the price from the original £79 ($79) after admitting it used software updates to deliberately slow down some handsets with old batteries.  It claimed it wanted to prevent unexpected shutdowns, which can often occur when the processor tries to draw too much power from an older battery cell.

But its failure to tell users about slowing down of phones provoked widespread outcry, with many replacing their batteries at full price to improve performance.  Apple now says it will refund the difference to these users using credits - but they have to be claimed. 

Apple also apologised for the decision to throttle iPhone performance in an open letter to customers.  ‘We know that some of you feel Apple has let you down. We apologise,’ the letter read. 

Disgruntled iPhone customers have filed at least 59 lawsuits accusing Apple of slowing down their phones so they would be encouraged to buy a new one.  The case could become one of the biggest legal challenges since it was first debuted in 2007, the Wall Street Journal reported.