Well the 8MP sensor is made by Sony that is the same chip in the Apple 5S & 5C.   Nexus 5 has optical image stabilization that does make a big difference in image quality.   Now the lens is the key to the quality.     About the 2,300 mAh battery the Nexus 5 with it's 4.95 inch screen is smaller than the larger LG G2's larger 5.2 inch screen.  So a smaller battery would be expected in a smaller phone that screen also won't use as much power.  It's expected that Kit Kat will improve standby performance for better energy conservation.  
If the Nexus 5 service manual details are correct, the Nexus 5 will offer up to 690 minutes talk time on CDMA networks, 405 mins on GSM, 530 mins on WCDMA and 230 minutes on LTE.
I just learned this that WCDMA. (Wideband Code Division Multiple Access). Wideband CDMA is a ... 384 Kbps. WCDMA was the 3G technology used in the US by AT&T and T-Mobile.  Before I saw that I thought  AT&T and T-Mobile used only GSM.