Where do we begin? G&E has posted many, many articles on this topic over the past year. To help consolidate all the information scattered across the site, I will be highlighting the more important topics and updating where necessary.
Some tips require you to be rooted or are more important to the rooted users, while the others are for everyone. Use this information when necessary.
We talked about calibration way back in August of 2010, and this is still one of the fastest ways to get better battery life. I tend to use the second method found at the link because it is faster.
If you are rooted, I would recommend that you calibrate your battery every time you flash a new ROM or kernel.
We've talked about this numerous times in the past: the internet can kill your battery. In general, as we pointed out a year ago, WiFi is better than 3G and 3G is better than 4G for your battery. If you are not using the connection on your phone (i.e., it's sitting in your pocket), turn it off!
Since Sense 2.1, HTC has given us Quick Settings in the notification pulldown. There are also similar toggles for AOSP ROMs. Utilize these options! You don't have to go into Airplane Mode, but if you aren't checking your Facebook, you don't need 3G sucking your battery. It takes less than 30 seconds to turn 3G (Mobile Network) back on via Quick Settings.
If you are still using Sense 1.0 on your HTC EVO 4G, then don't forget that many custom ROMs have begun incorporating Quick Settings into the notification pulldown. If you aren't rooted (or flashing custom ROMs), you can always add Widgets for these toggles (details can be found in this post from June 2010).
Regarding Bluetooth and GPS, it may not be necessary but I'd still recommend keeping those off unless you're using them as well. Again, it only takes about 30 seconds (or less) to turn them on when you need them.
App Killing and RAM "Tweaks"
G&E took a stance on task killers back in June of 2010. The big takeaway from that post was that "Android is designed to manage memory for you." However, there are rogue apps that will eat up your memory, which does kill your battery faster.
In Sense 3.0, HTC introduced a nifty Task Manager that will help you close the apps that always seem to stay open.
Other tips include using the Back button (instead of the Home button) to exit apps, since this actually closes the app. Users running ROMs that don't include Task Managers can go to Settings > Applications > Running services > select rogue app > Stop.
Taking app management one step further are RAM "tweaks." These are scripts or apps that rooted users can install on their HTC EVOs. A really good one for the HTC EVO 4G or 3D is V6 Supercharger and a new app called RAM Manager.
At the end of the day, your mileage may vary, so use what works best for you.
The Home Screen
This is probably a topic that gets ignored a lot. EVO users will get an optimized ROM and the best kernel, but then they make silly mistakes.
First, avoid live wallpapers. Sure, they look cool, but they kill your battery too.
Second, don't go crazy on the regularly updating widgets. Some widgets are fine, but don't clutter your entire home screen with every free widget from the Market. Remember, it's okay to have blank spaces.
And third, think about the accounts that sync on your phone. Does Facebook really need to update every 15 minutes? HTC has a cool Sync All widget. The best part is that you can turn all of your syncing off – trust me, people aren't commenting on your status 24/7 – and use this widget to sync at opportune times (like when you're on WiFi).
There are many apps out there that claim to improve battery life.
The best one to me is JuiceDefender. There are many versions of this app that have increasingly more features (for an increasingly higher price) but even the free version can give you 1.5-2x the battery life.
If you don't believe me, try it for a few days.
CPU clock managing apps can also be very helpful. I tend to underclock my phone and notice that it still performs great (with a little more juice too). SetCPU can be grabbed free from here, and No Frills CPU Control is free in the Market.
Some other useful apps can be found at this post.
Other Obvious (but not-so-obvious) Tips
If you have sub-par service, your battery is going to drain faster . . . sorry. My folks live out in the sticks – and I mean the sticks. When I go there, my phone lasts about 6 hours with a lot of the above methods in place. If you have poor cell signal, limit the amount of battery that your radios drain. Hell, if you aren't expecting a call anytime soon, flip it into Airplane Mode.
Speaking of Airplane Mode, which turns all cellular and mobile network radios off, this tool can really come in handy. If you're in a class or at work and you can't text – even for a second: Airplane Mode. If you're at the gym and leave your phone in your bag: Airplane Mode. Anytime you are away from your phone for an extended period of time: Airplane Mode. Or, you can even take it a step further and turn the damn phone off once in awhile.
The Extended Battery
The extended battery. Is it worth it? At the price HTC normally charges for it? Hell no. But, if you grab yourself a Seidio extended battery or even one of those Chinese ones off of eBay, then hell yes!
I have an extended battery for both of my EVOs (4G and 3D). Most days (like 95%) I can go from waking up in the morning to going to sleep on the same charge using the stock battery (thanks to the tips above). However, some days, I'm really bored and want to play games or I'm just checking Facebook a lot.
It doesn't really matter why, but everyone has days where they spend a lot of time on their phone. On those days, I'm thankful for extended batteries. If you consistently use your EVO every day (or even the majority of the time) and find your EVO dying all the time (despite your optimizations and tweaks), an extended battery is probably a good idea for you.
We all want more battery life; it's a fact.
But you have to remember that your EVO is a lot like a computer . . . a computer that has like 6 radios on it that constantly drain battery. You don't need to constantly monitor apps or try every kernel that works for your phone. Just make sure you calibrate your battery and only have mobile network radios on when you use them. If you're an average user, that should be enough to have a full charge last at least a day at a time.