I have been using my HTC Mozart Windows Phone 7 device for a few days now and while the OS is very good (see here) it also has some issues which most notably is the poor battery life of the device.
Update: This could be an issues with having Exchange/Outlook ActiveSync profile configured (even if set to manual sync) as removing the account profile from the phone seems to have improved the battery life. Stay tuned for more…
This is also an issues seen by a few other owners of Windows Phone 7 HTC Mozart devices which leads me to believe that this issue is not isolated to just my device or how I specifically use (or hold) the phone.





Interestingly when you setup Exchange/Outlook email it defaults to have a “arrive now” (a.k.a. push) email sync which basically keeps a 3G connected open and active at all times on the device. This configuration will cause a very large battery drain on any device (iPhone, Blackberry or Android) however as this is the default configuration with Windows Phone it may be the cause of some of these battery life issues. That being said even with push email turned off the battery life still appears to be an issue.

However battery life seems to no be an issues with other non-HTC Mozart devices so this would indicate the issue may be with the device and not the OS.
Interestingly that Windows Phone 7 will show both a WiFi and 3G indicator present at the same time where on iOS device you only ever see one or the other. This makes me wounder if the 3G connection remains active when the device is connected to WiFi thus drawing extra power. Certainly turning off all mobile data connections to the device improves battery life on the device so I do suspect that the power life issue is being cause by a 3G data connection that is some how being kept alive.
This is clearly a 1.0 OS and there are going to be some issues but I hold hope that these issues can be resolved as the phone does support software updates. Until then if you are experiencing issues then for now all I can suggest you make sure you turn off all push email synchronisations as this will be the number one cause of battery life issues with the device.