So you read the title and thought this guy must be a real noob. How can you short out your battery when all you do is twist out the old coil and turn in a new one, easy peasy. Here's the twist. I have a protank 4 aswell and I was changing out the coils. So as all things noob go, I forgot to switch the battery off and as I was trying to put the second lead into its post my finger hit the fire button. Saw some sparks and dead. Not me but the battery. It wasn't switching on. Swapped out tanks and no joy. Then went to Google and asked him a few questions but with no luck. Thought, oh well this is a trip to the store to see if they could fix it. At least my 521 is fully charged so I can keep on vaping. Took a few puffs and got an idea. Plugged the charger into the battery and voila it came back to life. So if anyone manages to short out their ijust s batteries. Plug in the charger and shock it back to life . Note to self, switch off battery.