If you note unusual/inconsistent battery drain in the Samsung Galaxy S8, S9 and perhaps S10 phones and there is no obvious apps draining the energy in the system power consumption tool here is the fix:

1. Old 2G networks: 2G networks use more energy for data transmission. Disable 2G fallback in the mobile networks menu.
2. Bluetooth: Some bluetooth network devices rely on bad protocol implementations that kill the battery of your phone even when not in use. Disable bluetooth in your phone and enjoy a much longer battery life.