[LG Optimus 2x] wapz:
This is a guide of how I have managed to massively extend my battery-life on the Optimus 2x. I personally use instant messaging like whatsapp and talk, and everybody should where possible, so I don't believe in turning off data during the day to save battery (sms is so 1999)! This are my recommendations to tune your battery-life from unacceptable to at least acceptable times (1 workday with quite high usage).

Items found to work especially well on the Optimus 2x P990

Use WiFi whenever you can, but disable when there are no networks you can join

- 3G seems to be by far the biggest drainer of battery-life, and WiFi idle seems to consume very, very little power. Make sure WiFi is *not* disabled when the screen turns off. Make sure to switch it off when you're not able to use a WiFi network however, to stop it scanning.

Set Network-Type to GSM (auto)

- Use the default dialer and select *#*#4636#*#*, select phone information and select GSM auto (PRL). Still allows for hsdpa data, not the maximum highest speed, but still quick enough for usage and extend battery life of some networks massively. If you want to be even more agressive, turn it to 2g only, but I find this too slow for casual surfing or internet usage, but if you only need it for instant messaging it should be good enough.

Disable gestures and orientation sensing

- Disable the specific gestures in the gestures menu and disable orientation by the button on the notification bar. Spare parts detects minutes of activity of the sensors during normal usage where it's not actually needed, so simply disable it when not using it from the notification bar (which is easy to do without switching apps anyway).

Make ABSOLUTELY sure your RIL matches your baseband

This is crucial. Without a matching RIL file (lge-ril.so in /system/lib) is ok, otherwise you will have a massive drain and problems with networks disconnecting all the time. Use LG GetRIl in the market to fix this if you cannot do it manually.

Check if your MicroSD card is detected when installed!

- I have issues sometimes with my MicroSD card being plugged in but not deteced, which causes my MicroSD card to become very hot, and my battery to empty in 3/4 hours completely. Reboot or remove and reinstall when it happens. Generally try to keep your phone keep as cool as possible, hot temperatures will decrease your battery-life.

Conventional and standard items for Android phones:

Check partial-wake usage in Spare Parts to find fauly apps!

- Check once in a while if there are any dodgy apps keeping your phone awake, causing your idle power consumption to be pretty bad!

Discharge your phone in a pattern of 100% to 20% and recharge

- Keeping cycles like this where possible, especially just after resetting battery statistics or installing a new rom, will eventually mean your battery will stay better for a longer period and you will notice your battery-life should be ok.

Make sure the minimum number of apps are running as services

- Go to Applications, Active services and find which unused apps you can disable.

Turn off Wireless Network Location if you are not using it

- Go to Location and Security, and disable use wireless networks.

Make sure not to use a task killer, especially not with automatic killing

- Sometime a taskkiller can be good to stop a app that hangs or causes issues, but make sure to not make it a default practice. To optimize battery usage, please tune the min/max of free memory managed by Android subsystem itself. Download Minfreemanager from the market, and set empty app to 96mb and content provider to 64mb and make it stick after reboots. This should make sure your phone will not slow down after a while of usage and enough inactive/idle apps are closed in the background.

Set Facebook / Twitter sync to once every 2 hours or more

- Make sure you don't let your phone sync that often, better to update it manually when you want to see it instead of syncing that often. Especially with Twitter having push now your direct messages will still turn up instantly even with slow synctimes for non-direct messages.

Watch out with Picasa sync

- Great feature, but dangerous since if it decides to start syncing when you are not on WiFi with bad reception, since it will mean it will sync potentially for a long time, destroying battery-life unexpectedly. There should be an option to sync this only on 80%+ battery only on WiFi but there isn't any, unfortunately.

Disable Google Latitude in Maps if not used

- If you need a longer battery-life, make sure you tell Latitude in Google Maps to not update your location (also see the point of network location), and make sure you sign out of it as well (so it doesn't update in the background if you are not using it).

I will update this and looking for good suggestions, please let me know especially about network-type GSM auto (PRL) and if it makes the same huge difference on your side. Also, another note, I am using 0405 baseband since I find best battery-life bundled with the RIL from a Vodafone Spain 0405 RIL as shared here.

Good luck improving your battery-life! :D