The HTC One X is pretty great, but its 1800mAh battery (not unlike the one on the Galaxy Nexus) is only OK. It turns out that HTC itself made something of an error in judgement when putting together that shiny new software. Due to an errant APK location, the native NVIDIA power control app (you know, the thing that makes that magical "5th core" work to save all that battery life) wasn't working properly. HTC should have a fix out soon enough, but in the meantime, the fellows at XDA have a fix for you.
It's a very simple process: all the ADB function does is move a copy of the "NvCPLSvc.apk" into its proper place in the system/app folder, instead of the system/bin folder. Noted Android developer Mike1986 noticed the problem, which should only affect the international version of the HTC One X. You just need the ADB files from the Android SDK to enable the fix - root isn't even required. If you do have root, you can use an app like Root Explorer to manually move the app yourself. Either way, reboot and you're ready to go.
Users are reporting between 10 and 20% better battery life, which is nothing to sneeze at in a high-powered phone that got about ten hours of active use and 14 hours of on-and-off use in our review. That's nothing terrible - we've seen far worse after all - but it's also less than we might have hoped for. The excellent standby time of the One X shouldn't be negatively affected by this mod. If you're the cautious type, you might want to just wait it out. HTC will probably apply the change themselves in an update sooner rather than later.