As part of our revamped battery test smartphones on IT Pro we now test the battery in four key areas - music playback, HD video playback, gaming and web browsing. We measure how much each activity reduces battery life by over the course of an hour - giving you an idea of the activities that will sap the battery..
All tests are carried out with 75 per cent brightness and the Wi-Fi turned off unless stated.
With a 2,600mAh battery pack powering the M8 helped the device compete with smaller 4iniPhone 5sin most tasl.
The M8 was more economical than the iPhone when it came to gaming. The Qualcomm APU in the M8 used 15 per cent less power than Apple's custom design over the same period.
The only area where the iPhone 5s was significantly better was when it came to HD video playback - with the HTC M8 using double the power (18 per cent) per hour.
The M8 does have a couple of trick to extend battery life. There are two power saving modes which can be set to turn on automatically or activated manually. The regular power saver reduces CPU usage and screen brightness to conserve power. It also turns off vibration feedback and puts data to sleep when you switch off the screen.
If you need to stretch the battery for as long as possible there's an Extreme power saving mode. This changes the interface - keeping just the core dialer, messaging, mail, calendar and calculator running. It also switches off the pedometer. You can specify mode you reach 20, 10 or 5 per cent battery power or turn if on manual whenever you like.
When you reach a plug, you can also take advantage of the quick-charging capabilities of the M8 - HTC claims it will recharge to 80 per cent in one hour.
