I've used aftermarket batteries in my Roombas for years. Last one I bought that I've been using in one of my 980's for about two years:

https://smile.amazon.com/gp/product/B078XNPTXR/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It is normal for batteries to fail after two years of use.

I use one of these in a 980, so should work for you.

https://smile.amazon.com/gp/product/B078XNPTXR/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1