Before You Complain About Battery Life...
Do you think your battery life sucks? Worried your battery is defective?
Here's what I did to better understand my usage and decide if my battery was defective, and if I could live with the battery life of the Droid. I did some searching and reading of different threads and now I do the following:
1. Of course make sure the screen brightness is as low a level as tolerable. I avoid auto brightness personally, and just use a widget on my home screen.
2. Turn off things I don't need like, wifi, bluetooth, and gps.
3. Pay attention to apps that want to update in the background and/or follow my location. Choose times reasonable for updates for widgets and email syncing (although all my mail is push).
4. Monitor usage for a few days using one of the apps I list below to not only get a mathematical, quantitative feel for your usage, but also to identify apps that might be running a muck.
The Droid has the battery usage screen accessible via Settings > About Phone > Battery Use. This usage screen tells you what percent of your CONSUMED battery different things account for. Usually, display is the biggest offender.
But there's another screen in the SDK that can't be accessed through the settings menu. It's the battery history screen. These are some apps that I have found that will link to this history screen.
Spare Parts - Free; most of the features don't work on the Droid, but the battery history link works.
BetterCut - $1.99; create an activity shortcut and choose 'Battery history' once the list loads.
Battery Status - Free and paid versions; put the widget on your home screen and tap the percent area and choose history from the pop-up status screen
Battery Left - Free; run the app or tap the widget and choose history
The battery history screen will tell you the actual percent of time spent with the phone running (as opposed to sleeping), the display on, wifi on, wifi running, and bluetooth on. Tapping any of these will give you the actual time for each. This time can be based on time since last unplugged, total, or since last boot.
Another screen gives you your partial wake usage by application, so you can find out what applications are waking your phone up from sleep, and how long they have kept it awake for. This is very useful for identifying apps that have run a muck, or for just seeing how long those widget updates or email checks keep your phone running for.
Another screen tells you your GPS usage by application, so you can see what apps are using the GPS and how long they used it for.
There are other screens as well, but I don't really use them, but you may find them useful.
All of this is important to know when trying to understand your phone usage. It's not very easy to help someone when they post, "Help, my battery life sucks and I only use my phone light for x y and z!" Usage depends on the person, what is light or heavy to one person may be normal to the next. Actually looking at what different features of your phone are being utilized and for how long is a much more qualitative and quantitative way to gauge your battery life and figure out if you have a problem and might need to return your device or your battery.
After spending some time using my phone normally with non-critical things (for me) turned off like GPS, WiFi, and BT and only enabled when I want to use them, I now have a good gauge of how long my phone will last in a typical day. Now I'm seeing how leaving GPS or BT on all day affects that. I'm monitoring which apps I want to use GPS if I do decide to leave it on all day. This way I can decide if its worth the battery hit to leave GPS or BT on all day and how I can minimize the damage if I do leave either on. I've gone from turning everything off and nothing updating to now fine tuning what I want to update and how frequently, because I now know how it affects my battery life.
I want to use the features of my phone, not turn it all off to save battery. It's just a matter of finding the balance of what I want on and what I'll settle for leaving off.
Sorry for the length, but every day there is a battery related question, so I thought I'd share how I helped ease my doubts about my own battery life. I now know how I use my phone normally and have decided to get a spare battery to have for those times when I know I won't have a normal day of usage. And I'm no longer worried that something is wrong with my battery or my phone.
ETA: It looks like just having GPS enabled has no effect on battery, based on my limited, non-scientific testing and the inputs of others. Of course you still need to find the balance between letting apps use the GPS, because GPS is still a battery hog, but I don't think just having it enabled in settings has an effect.