The ‘Extreme Power Saving mode’ is one of the best-known features of HTC. This mode allows the phone to retain the battery power for 15 hours, even when the battery life is just 5 percent. In this mode, the phone goes into hibernation phase and does not search for network online, when the phone is no stand-by mode. The case of ‘extreme power saving mode’ turning missing is one of the main features in the HTC One M8 handsets shipping to the US. One of the reasons is that the version of the phone that has been shipped in the US, probably carries the software version that is outdated and does not carry the ‘extreme power saving’ option.
To see the ‘Extreme Power Saving Mode’ option in your HTC One M8 phone, wait for the software update. You can check for updates by going to Settings – Software Updates – Check Now. The HTC software version that has the ‘Extreme Power Saving Mode’ should have version 1.54.401.5 and more.