Hi9 Pro - Battery sudden discharge?

I have a problem with my Hi9 Pro, since purchase last October. From fully charged to around 25%, everything is fine - it then suddenly drops below 20%, then rapidly goes below 10%. I have replaced rhe battery and there are no open apps causing heavy useage. Could this be a hidden app causing heavy battery useage? I have looked at Settings, Battery, ‘Battery useage data’ is not avilable.
Any ideas?

I have exactly this problem on a new Hi9 Pro. Everything is fine until the battery gets down to 20-25 percent. Then it starts racing down to zero. Really racing, getting to zero in about a minute. I’ve never seen anything like this.

I think that since others have this problem, Chuwi should look into it - I have also spoken to another user, with the same problem. I believe that there must be a background operation running which causes this sudden battery discharge.
Can Chuwi please look into this.
Best regards,