A raw file from my P2V is 27.5 MB the card has roughly 15000 MB free most of the time so it can't be an issue
You should try for 20 dB see if you get more range I doubt it that it can cause any harm to camera/wifi system. Either way it has a temperature protection as stated from DJI in the manual ... it will automatically turn off to cool itself. I'm now flying at 20 dB all the time
If you see that huge drop in battery that fast I would say that battery its on its way to the battery cemetery. It happend to me with lots of other devices and when huge battery drops like that it will die out eventually. I would honestly not use it anymore since it can be dangerous to your Phantom and to others. I'm not sure about battery life cycles ... DJI I think says 300 tops then you can replace it. Some were crying on the internet that 100 cycles and its gone. I would honestly would love to get 250-300 cycles from my batteries. (I only have 2 since they are expensive for me).
One has 20 cycles and the other maybe 10 so they are "new". Regarding this I would like to ask you if you leave the battery turned off inside of the P2V ? or you remove it ? I would like to leave one fully charged in the P2V but turned off. Do you think it will discharge or anything ? since its turned off.