@martygp95, Yes, powering the Sentinel with a 4S is fine. Just be sure NOT TO FLY with it. The tuning for the drone was done around the 3S and if you attempt to fly with the 4S, then there could be detrimental flight-performance.
The APM on the Sentinel can handle 2S-6S [2 cell (6.4V min, 7.4V nom, 8.4V max) 6 cell ( 19.2V min, 22.2V nom, 25.2V max)]. You can find info about the APM here
Hope that helps