Calls Dropping.

hello! i currently own an iphone xr. me and my friend usually like sleeping or talking for a long time on facetime or audio call. the sad thing is everytime we do, once it hits maybe like 4 hours and a couple of minutes. my iphone automatically ends the call? my friends phone doesn’t and he keeps it charged and stuff while we’re talking so it’s just me and i’m confused. how do i stop it from doing that? i don’t want a time limit on my facetimes pls!