If you were in the first batch of Beta85X maybe you got some ESC failure or fire with your Beta85X.

Fortunately, BetaFPV identified the problem and take into their charge the changement of the ESC board or the quad (if everything burned).

They have detailed the problem on their blog and they will improve their quality test to avoid this kind of problem:
https://betafpv.com/blogs/blog/announcement-on-85x-fire-accidents

So if you are in this case, you can follow the step in the next link to see what you could do with the warranty:
https://betafpv.com/blogs/blog/for-customers-that-bought-the-first-batch-of-the-beta85x-from-our-website

If you have a Beta85X of the first batch, it is strongly not recommanded to use any 4S, and if you bought a lot of 4S LIPO for this quad, BetaFPV will send to you a new ESC board that supports 4S:
https://betafpv.com/blogs/blog/for-customers-that-bought-the-first-batch-of-the-beta85x-from-our-website

It means that they fixed the problem and are already producing new ESC board to support 4S LIPO. I think they handle correctly and as a professional company the problem for all customers.

This quad is still a beast and really cool. I will post my review asap.