||The alternative advanced lead-acid battery is one of the promising ultrabattery. The ultrabattery is also reusable battery consisted of electrodes, AGM separator and electrolyte. As the important component of the ultrabattery, the requirement of an ideal separator is required to have high absorbility, which is the ability to absorb the electrolyte. In this study, we studied the surface of the AGM separator was etched using atmospheric plasma. As a result of plasma treatment according to time and RF power, a high BET specific surface area value (3.5m2/g) was obtained. The etched AGM separator were characterized with EDX, area resistance, pore size distribution, absorptive properties and single-cell performance.