I have seen a few people suggesting the possibility of swapping the LG G2 battery into the Nexus 5, which reminds me of the Atrix HD. You could swap the 1780 battery out of the Atrix HD and throw in the 3300mah battery from the Razr MAXX, almost doubling the battery life. The batteries were almost the same size except for an increased thickness.
Naturally I also dreamed of putting a beefier battery into my (soon to be arriving) Nexus 5, however I come to you now to destroy those dreams.
I pulled up some old FCC battery pictures of the LG G2 battery, model BL-T7, and the Nexus 5 battery, the BL-T9.
As you can see in the attached pictures, there are 2 major issues that will prevent a battery swap from happening:
LG G2 BL-T7
Nexus 5 BL-T9
The LG G2s battery is 2 millimeters thinner, however it is also 7 millimeters wider. This is a rather large difference, and looking at photo 3, there is no way in hell you are going to get another 7mm of height.
Secondly, the placement of the cable where the battery attaches to the phone is very offset. You would need some sort of extender in order to get the connector to reach, would would be another chore in itself.
LG G2 battery:
Nexus 5 battery:
Nexus 5 with cover removed:
I realize my measurements might not be perfect, but I highly doubt they are more than 1-2mm off.
It really is too bad... because it looked like the N5 has a few mm of thickness to spare.