[myTouch 3G Slide Q&A, Help & Troubleshooting] r0man:
I see lots of posts around the Interwebs complaining about battery life on smartphones (specifically Android ones, since I don't hang out on sites that are aligned with evil Apple), so I decided to consolidate my knowledge for people with Slide's to improve their battery life.

DISPLAY

This uses about 80% of the power according to battery use on auto-brightness. On a bright day I can read the screen at about 1/5 position on the brightness bar which cuts down heavily on the battery use.

There's not much else we can do to cut down on screen power usage, so moving on.

CPU

This one requires SetCPU, I strongly urge you to buy it from the Market (it's just a few bucks IIRC) and supports the AWESOME dev. If you're cheap just go download it from that link.

Once you have it you'll want to set up profiles! So click profiles, check the box next to the Sleep profile and choose 480,000/480,000 with ondemand scaler! I have no idea if it actually changes anything but the placebo effect is nice. Next back out of that and set the CPU governor to performance. What this does is clock the CPU to 600mhz constantly instead of scaling between 480mhz and 600mhz as the additional power is needed. It cuts down on choppiness while barely increasing the amount of battery required (in my experience the Slide tends to jump up to 600mhz when I'm not doing anything anyway).

Sync

Turn auto-sync off or set the sync intervals to the highest number possible (once a day I believe). It takes power and most of the time doesn't download anything important. If you really need some data just go and hit Sync Now and, well, it syncs.

Autostarts

There is this nifty little paid application in the market (costs like $1.25 or something) that you absolutely need: Autostarts

Basically applications launch when triggers are triggered, alot of these are pointless and just take up RAM and power.

These are what I have disabled:

After Startup

{Any 3rd party apps that aren't widgets}

Calendar Storage

Download Manager

Voice Dialer (unless you, yaknow, use it)

Maps

Mail

Calendar

HTC Media Uploader

My Account (unless you like the power alerts that take up power!)

Connectivity Changed

Download Manager

My Uploads

HTC Media Uploader

Genius Button

Media Mounted

My Uploads

Application Installed

Voice Dialer (wtf?)

Pico TTS (sem-wtf?)

Application Removed

Voice Dialer

Application Replaced

Maps (lolwut?)

Autokiller

There's an app called Autokiller, it changes the internal task killer's settings as to when to tell an app to shutdown (at stock settings this is almost never).

I use the moderate preset, but you may want to increase it if you never want to have to manually kill a task. Note that this method tells apps to cleanly shut down so data is saved (such as the page you are on in the Browser)

Additional Settings

In Mobile Networks set to GSM only (no 3G)

Turn GPS and WiFi off when not in use

Turn always on data off

Use a silent or vibrate alert method instead of sound alerts

Turn off your screen whenever you can

If you flashed ENG-BUILD flash the updated RADIO!!!!!!!

Protips

Do several battery cycles every 6 weeks (Charge to 100%, discharge to 0%, charge 2 hours past green LED while phone is off)

Espresso is heavy duty stuff, use a non-sense ROM for additional speed

Charging via USB takes significantly longer than charging via AV

Live Wallpapers will use lots of battery

Use wallpapers formatted at 480x320

Limit the amount of widgets you have to around 5 (unless they are from the same app, like Beautiful Widgets) they constantly refresh and do their thing in the background

I learned most of this thanks to enatefox's guide which I modified to suit the Slide, a coffee fueled mind, and general observations. If you have anything to contribute please let me know and I'll add it!