It doesn't take much searching on Google to find out that the battery life on a couple of the top-of-the-line Windows Phones -- the Nokia Lumia 920 and the HTC Windows Phone 8X -- are less than spectacular. Forums are rampant with angry user complaints about how quickly their phones are draining, turning their phones into useless bricks by each day's end.
Decreasing brightness and disabling Wi-Fi when it's not in use are a couple obvious tips, but (like almost any piece of Windows software), there are other settings buried deep in your phone's system depleting the precious life of your limited battery.
On your phone, head to Settings, and adjust the following options. It goes without saying, but if you use one of these features, keep it enabled.
Boost battery life on Windows Phone 8
Wi-Fi: Here, tap on Advanced, and uncheck "Notify me when new networks are available," and "Send information about Wi-Fi networks."
Tap + Send: It's unlikely this feature gets used much -- turn it off.
Email + Accounts: For each account, adjust "Download new content" to the lowest frequency you're comfortable with. If you can, choose Manually. Otherwise, choose Hourly. If you choose Manually, new e-mail will only be downloaded when you access your e-mail.
Backup: Backing up your data is important, but it would be less of a drain on your battery if you did it manually. To do so, disable each backup option. Then, when you're ready to back up your data, re-enable those options.
Phone Update: Uncheck "Automatically download updates." Your phone will still notify you of an update, but it won't download it automatically, a task that is a huge inconvenience when there's no charger nearby.
Back in the settings menu, swipe over to Applications. Here, tweak a few important things.
Background Tasks: Listed here are any that have permission to run in the background. Go through this list, and block any you don't absolutely need quietly fetching information (and draining your battery.)
Games: Turn off "Connect with Xbox" and "Sync game requests." Again, if you use these features, leave them enabled.
Music + Videos: Turn off "Connect with Xbox Music" and the cloud connection feature.
With these changes, you should see a significant increase in your phone's battery life. If you want even more battery-saving tips, check out this post by a WP8 user who kindly offers dozens of ways to save battery life (not without sacrificing features, of course.)