Honestly, can't give a solid impression because I'm running it VERY lightly and without a SIM. But, so far it looks to be real solid. If you look at the Moto X, everyone was afraid it'd have bad battery life because the battery was so small. Well, the Moto G's is not much smaller and I think going all day is no sweat.
Quite a bit on XDA if you want to go through that massive thread:
Post your battery - xda-developers