I’ve owned my Desire for around 3 months now, so I'm hoping I'm a reasonable position to pass on some advice about saving battery life.
A lot of these tip and tricks have been trial and error and have been gleaned from a variety of sources as well some playing about by myself.
I’m not saying that this list is exhaustive, but its as far as I've got so to-date. Please feel free to let me know about any other little tips.
1. Disable Always-On Mobile Data.
Settings, Wireless and Networks, Mobile Networks, untick Enable always-on mobile data
2. Turn off Wireless Network Positioning
Settings, Location, un-tick Use Wireless Networks
3. Turn off GPS
Settings, Location, un-tick Use GPS satellites
4. Turn off Bluetooth
Settings > Wireless & networks > Blue-tooth. Both the above (GPS, Blue-tooth) can easily be switched on/off when required by adding the HTC Power Widgets to your home screen. “+” > Widget > Settings > Airplane Mode, Blue-tooth, GPS, Wi-Fi etc
Use a dark or mainly black wallpaper and DO NOT use Live Wallpapers. The AMOLED screen burns battery when displaying bright/white colours.
5. Install “Brightness Level” widget from the market and set brightness to 25%. Should be fine for daily indoor use and you can always up the brightness to 100% in sunlight if required. I’ve found “auto brightness” keeps the setting too high throughout the day, especially indoors when not required.
6. Install “Juice Defender” from the market, but don’t install Juice Plotter (i found this to use more CPU that I liked). Juice Defender automatically turns off 3G(APN) and Wi-Fi when you turn the screen off, but automatically wakes up every 15 mins in background to sync your mail etc or when you turn your screen back on, but SMS and call signal stays on 100% of the time. There is much more to the app than that, but that's the instant battery gain, switching off 3G and Wi-Fi automatically when you don’t need it.
7. If you are not using Google calenders, remove then from your sync process. (Settings>Accounts and Sync>Your Google Account> un-tick Calender)
8. Install “Spare Parts” from the market place. Use “battery history”, “partial wake usage” to see what processes are taking up CPU time.
9. Install “SystemPanel Lite” from the market place. After a day of running you’ll be able to see which processes are using more CPU time than others. This is how I found Juice Plotter above. I also found that some apps that I'd installed were poorly written and just hang about taking CPU time, which obviously in turn eats away at your battery. For example, I'd downloaded a Wall Paper app, but it was chugging away in the background eating CPU cycles, you wouldn’t have thought that would you?
10. Use the “BACK” button to exit apps rather than just hitting “HOME”. Using “BACK” appears to store them as “inactive(cached)” apps, whereas “HOME” just leaves the app as “Background” task which “appears” to use more CPU. This is something I've only been playing with for a day or so, but seems to make a difference and is a good habit to get into.
11. Disable automatic time and date settings ('Settings -> Date & Time -> Uncheck Automatic').
1) Turn your device ON and Charge the device until the light goes GREEN
2) Unplug the device and Turn the phone OFF plug it back in and again charge it until it goes GREEN
3) Unplug the device Turn ON and fully boot the device. once its booted turn it off - plug it back in and charge it again until it goes GREEN.
4) reboot and use
13. Root your phone
This is a scary suggestion for those who don't like to tamper with their new toy. But "rooting" my Desire (in essence allowing you to modify your phone away from stock HTC builds) has worked wonders for my battery. This has happened because the alternative Froyo build i've put onto my phone has the operating system tweaked to use less juice.
The build I currently run is: http://android.modaco.com/content/htc-desire-desire-modaco-com/317191/20-sep-r9-wip-modaco-custom-rom-for-htc-desire-online-kitchen-2-2-froyo/
Disclaimer: attempting to root your phone is entirely at your own risk. (all details of the risks are on the Modcao site)
My summary is that recommendations 1 to 11 cause a nice uplift from stock settings.
Point 12 then increased things even more, which i didn't think possible.
And finally, the new root build has squeezed even more daily life out the battery.
There is no definitive list to follow regarding battery life as the phone is so configurable that everyone has different apps and usage patterns. But all of the above have left me in a far better position that I was when i first opened the HTC box 6 months ago.
Some people have said that Juice Defender has worked for them and any others say its the best thing since sliced bread, me included. Like any of the tips in this list, they are just what i've come to find help me and my usage pattern. Try them, if they don't work for you, just switch back to how you had it before.
Feel free to leave comments or further suggestions how you save battery.
Below is a nice dark design that I've been using as a wallpaper/background on my Desire. Click on the picture to see it full size, then either save as to your PC or long press on your Desire and save to the phone. You can then choose the pic in settings>Personalize>Home Wallpaper
I have now ditched "HTC sense" builds and gone for vanilla Android. This Gingerbread build is so minimal that battery life is even better once the minimal build is on and all the above tips are followed. (although I find I no longer need Juice Defender.... but each to their own)
For those scared of rooting, the XDA forum gives easy to follow instructions.