Your Tenderbuck Electrostimulator has a standard 1.3 amp hour lead-acid battery. Proper maintenance of the charge can increase the lifespan, but if your battery needs to be replaced, we've got you covered. When you order the battery from us, we will include a strip of anti-vibration foam on the side of the battery. To replace the battery, simply remove the four screws on the back of the unit that hold the halves of the case together. Make sure to connect red to red, and black to black. Reassemble, making sure that the electrostimulator leads are not pinched and that the retaining grommets are properly seated in the case.