All of our Femme Tens and Lady Tens Maternity TENS / Obstetric TENS machines use a standard 9v battery.
Here you can buy a spare battery for use should the battery that we send with the TENS machine be used up during labour.
Typically, a battery will last around 6 - 8 hours, but this does depend on it's use, and, of course, no two labours are the same !