Mine is a combo 12 volt/ 120 volt heater. It is rated at alot more wattage with 120 volt than at 12 volt and it gets hot faster as you would think. I think it's 450 watts at 120 volts and 280 watts at 12 volts. It gets hot pretty fast at 120 volts. You won't leave your hand on it but it won't blister you just touching it if it's on the bottle. It might if it was just unattached and sitting somewhere.
My Edelbrock 400w heater has a warning on it that heater could reach 300 degrees!!
I have a transducer on mine and will bring mine from 600 to 1000 in about 15-20 min and shut off automatically. I have killed both my batteries with it. now I only use it in the pits while on high charge.
There are two seperate ways to start the heating process within the one pad with this type of bottle heater (110V or 12V / 16V. If you don't have some type of sensor (pressure or temp) to turn the pad off with either way of starting the heating process, then yes someone will be in deep shit. Especially if the bottle is full or almost full!!!
I have come close to fuggin up with this type of heater pad (w/o a sensor of some type) and i'm just glad that my mother bottle wasn't full!