Update: gpu rendering actually decreased battery life, or so I think. I'm going to test it a bit more to be sure though. The combo of the kernel (from .283) and baseband (baseband 36) with the .42 firmware build caused a huge improvement, however. Before, my battery stats showed the Android system and cellular transmitter using the most, but now it's far less and most of the power used is from the home launcher. Battery life still isn't as good as what I got with 2.3.3 during the summer, but FAR better than on regular .42 firmware with the .42 kernel and baseband.

I suspect the difference is my theme, which I didn't have before, xloud, the bravia engine mod, and the newer home launcher version.
The home launcher never showed that much drain on older firmware versions, so I'm guessing the newer one uses more power.

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[ORIGINAL POST]

Well guys, I think I found a solution. Some Arc users decided to mix kernels and roms, and discovered a battery fix.

Basically, you install the oldest 2.3.4 version (.283? Something like that anyway) using flashtool, then flash the .42 firmware, but you tell flashtool to exclude the baseband and kernel.

As a result, you have a newer firmware build with an older (better) kernel and baseband.

That way, you end up with battery life how it used to be before the update, BUT you can use themes and mods that are meant for .42, which is the most popular version. I've tested this technique out, and everything is working perfectly.

I already rooted, installed the locked bootloader cwm, flashed a theme, some mods, and a boot animation. Some of those were .42 only, and worked fine, so the kernel must not matter.

I'll have full battery results in a couple of days. The arc users who did it got amazing improvements though.

Also, I enabled gpu ui rendering using the xperia tweak app. Not sure if it's caused by that, or the kernel/firmware combo, but my browsing and general OS use is RIDICULOUSLY smooth right now. I can honestly say I have never seen this phone this fast in the time I've had it since last May.

Sent from Asgard
Devices

LG Nexus 4 | Stock 4.2.2

Samsung Galaxy S II GT-i9100 | Wanamlite v14

Sony Ericsson Xperia PLAY | JokaWild 2.5 | DooMKernel v13 -Sold

Samsung Galaxy TAB 10.1 4G | Stock ICS -Sold

Firmware Collection for Xperia PLAY | Flashtool | JokaWild ROM | DooMKernel | SiyahKernel for GSII | CheckROM for GSII