I need a replacement battery for my C90S notebook.

Batteries for the ProMagix x20/x25 notebook (Asus C90S) are available through various online retailers like the ones below.

Asus eStore

https://www.avadirect.com/plist.asp?keywords=c90s+battery

https://www.btotech.com/_e/Batteries/product/c90_battery/Asus_C90s_Battery.htm

NOTE: Buyer Beware! As always, when making online or offline purchases, check into the return policies for restocking or shipping related fees.
We are not affiliated in any way with the retailer(s) above and cannot be held responsible in any way for purchase problems.