From my experience, i get great battery life on mine running stock.
Sometimes I reboot because of a qcom-camera-something-like-that bug draining battery or whatever it is but no serious deal breaker
I had one time 1 day 14h @ 44% with light usage, wifi turned. Most of the time i do play a lot, read mangas, have whatsapp, hangout, facebook, snapchat, instagram and all these apps installed pushing notifications, It still gets me through the day easily.
I was worried about the battery when i bought it but keep in mind, even if the LG G2 has 3000 mah, it has to run all LG services and tricks like "double tap to wake up", this device is PURE Google. See it like an enormous engine with only wheels, no fancy sh*ts, it's up to you if you want to make it lightweight or heavy as ...
Anyway if you're still concerned about the battery life, get a wireless charger for 40 bucks and put it where you stay the most (desktop at work/next to you computer). You will just have to lay it down to make it charge with no efforts