This is a brand new Asus C23-UX21 replacement battery. This battery can be easily installed yourself. It does require you to unscrew the cover on the bottom of your laptop to access the battery. This battery ships fully tested and ready to go. Inside the Asus C23-UX21 battery are South Korea's best Lithium-ion rechargeable battery cells. The superior battery cells will provide longer run times between charges as well as a longer service life than cheaper batteries. In addition, Li-ion batteries are not subject to the memory effect common with older battery technology. This means you can recharge your laptop any time without diminishing your battery capacity. This laptop battery replacement is typically superior to the original battery and is 100% compatible with your Asus UX21 notebook computer. The battery is individually tested before shipment and backed by 30 day complete satisfaction guarantee and a 1 Year warranty.