Airlines allow you to carry on your own defibrillator, but they may not allow you to bring its battery. Check the size of your automated external defibrillator's battery well before your flight so you have time to make proper arrangements.
The Federal Aviation Administration allows you to carry on up to two batteries with a maximum of 160 watt hours per battery. If watt hours are not listed on the battery -- as a number followed by "Wh" -- then calculate watt hours by multiplying the battery's volts by amp hours. It's recommended that you carry on your batteries instead of checking them and alert the crew; attendants can get to the batteries in case of fire. If your AED is too powerful to bring on board, ship your batteries ahead of time and bring your powerless defibrillator.