Bit of a bump.
Just got the 3800 battery yesterday for the Gnex and wanted to chime in on it. While a lot are blasting it for its size and deformed look, I actually like it. The naked Gnex is too thin for me, and I have a little issue reaching the top of the screen (specifically to pull down the notification menu) with the way that I held it. With the extra depth to it now though, I find I'm able to easily reach the top, and it just feels so much more comfortable in my hand. Another minor plus is when using the Gnex for music or movies, I found that I'd sometimes cover the speaker hole, nearly muting the sound. With the hump ending just above the speaker though, I've found that its rather difficult to cover the hole, accidentally or on purpose.
The battery life itself, I'm guessing I've still got a ways to go to see it shine. I've only had one good charging cycle (unpacked it yesterday, ran it dead, hooked it up to AC, booted into recovery, wiped battery stats, allow to fully charge +3 hours) and I'm sitting at 83% after 3 hours and 40 minutes off the charger. I've only mildly used it today for any sort of tasks, but I've racked up 48 minutes of on screen time at about 20% brightness. This has used 48% of the 17% I've used. I would of expected this all to effect the battery a tad less, but perhaps I came in expecting more than I should of. Voice Calls came in next at 18% for a 14 minute phone call, everything else was 8% or lower.
At this rate, I can prolly make it through a work day without issue (30%+ after the days over) with moderate use, but I was expecting to be able to really blast this thing for a good six to eight hours a day, streaming, browsing, etc. With such moderate use hitting it hard, my expectations may be a bit overshot.
For what its worth, I'm using GummyNex-TORO v0.7.6, the kernal that comes with it, undervolted to 1350 MHz - 1175 mV, 1200 MHz - 1125 mV, 920 MHz - 1025 mV, 700 MHz - 925 mV, 250 MHz - 850 mV, and Juice Defender Ultimate set to 30 min sync cycles when the screen is turned off.
Hope this helps anyone on the fence concerning getting the battery. Its not quite the game changer I thought it'd be, but I'm still pleased with the overall benefits I've gained.