Apple engineers are contacting some iPhone 4S owners to try to solve problems with battery life on the new device, after some people have seen dramatic drops in longevity compared to previous models.

One owner has told the Guardian that Apple contacted him directly and asked him to install a monitoring program on the phone to try to diagnose the problem, which is so far unexplained.

In its data sheet for the iPhone 4S, which was released earlier this month, Apple quietly noted that the standby time for the new phone would only be 200 hours - compared to 300 for the iPhone 4, and 250 hours even for the original 2007 iPhone. The company did not offer any reason when asked why by the Guardian, but noted that other lifespans such as 3G talktime were as long or longer than previous models.

One owner who was contacted by Apple told the Guardian: "My battery life was extremely poor - 10% drop in standby every hour. I noticed that the usage figure was roughly half that of standby, even when the phone was not being used, so I assumed something was crashing or running in the background. I switched off all the new features including Siri and location services, but it was still really poor. I also tried setting up a clean phone with no apps but it is still really poor.

"I then got a call from a senior [Apple] engineer who said he had read my post and was 'reaching out' to users for data and admitted this was an issue (and that they aren't close to finding a fix!) and asked lots of questions about my usage and then asked if he could install the file below and that he would call back the day after to retrieve the info. I extracted the file from my Mac after a sync and emailed it to him. He was incredibly helpful and apologetic in the typical Apple way!"

Users of the iPhone 4S have been surprised by how rapidly the phone's battery appears to drain, especially compared to the iPhone 4. The 4S incorporates a more powerful dual-core processor, the A5, than the iPhone 4, but the same amount of RAM. According to iFixit, the iPhone 4S has 5.3 watt-hours' capacity - 0.05Wh more capacity than the iPhone 4.

In some cases the short life has been blamed on corrupted contacts imported from Apple's MobileMe or iCloud services, or from Google's Contacts list; deleting and then reinstalling them sometimes seems to fix the problem.

The problem has generated huge discussions on Apple's support boards, with some people finding that backing the phone's contents up to their computer and then restoring it improves the life.

The Guardian's own tests on an unrestored iPhone 4S using Google Contacts and MobileMe suggest that the phone drains fastest when mobile data is switched on, while Wi-Fi usage makes little difference to battery consumption. Neither location services, which try to orient the phone based on Wi-Fi and mobile data information, nor the voice-driven "assistant" Siri, appear to affect battery drain particularly.