Warp can be a calm background process when phone is idle. See screenshot from 14:00-14:45 (and earlier when other apps were lightly in use, not shown in detail).
Warp then switched to eat battery mode whilst the phone remained idle (10% in 2 hours). See screenshots from hours 14:45-16:45.
Later (about 20:30) I became suspicious and switched to DNS only. Note no battery usage for 1 hour 21:00-22:00 in last screenshot
The iPhone X (iOS 13.1.3, V4.2 (1911251900.0)) was in same physical location (on wifi with cellular available) and environment throughout.
WARP may be desirable, but a non flat battery wins!!