See [Internal SSD Installation Guide] of our web page for changing internal battery. It is not very easy, but not very hard. Although it's major topic is on changing internal SSD, you can also see how to change the internal battery. Currently internal battery is not listed anywhere because internal battery might be OK at least more than a year, but later we will have it in out web shop or our partners web shop. It might be $50 + shipping($50 from Korea to Global). If any body need it NOW, just contact us through our CONTACT(https://www.clouzen.net/contact).