If it's in the same room, it not unattended. However I get your point and personally, I also keep them in a fire bag when they're on charge...
It doesn't say that anywhere under the battery heading in the P4 user manual (V1.0 or V1.2) but then I had my first ever look at the "PHANTOM 4 INTELLIGENT FLIGHT BATTERY Safety Guidelines V1.0" and yes halfway down page 2 it does say you should never leave the battery unattended during charging and it also says don't charge on a flammable surface such as carpet or wood. Now how many of us follow those instructions to the letter, I had never even seen them before now. I would have to take mine to the shed and although there are plenty of jobs to do across there I suspect the only reason I would be monitoring a charging battery is if I only wanted to charge it to 50% for storage.
I assume your fire bag isn't transparent so you wouldn't actually know anything was wrong until you smelt or saw smoke. Also I would have thought ventilation was important for cooling a charging battery, I would not want to keep it in a fire bag while charging.
They do not generate any significant heat when they're being charged; certainly they're nowhere near as hot as when you remove them following a flight. Additionally, I think you'll find it's pretty good practice to keep LiPo's in a firebag when charging.
Yes smoke or flames is way too late but if you can see the LEDs you have some idea of how things are progressing, if any errors have been generated and I like to remove the battery from the charger at the transition from 2 blinking to 3 blinking LEDs which is 50% for storage. That is all more difficult if the battery is in a bag.
I also remove them at 2+1 for storage, but I'm referring to charging when I'm going out to fly, and the batteries and I are in the same room.
