Here is my RB433AH system health. I purchased it when they first came out, so it is an early version, if there is such a thing.
[admin@MikroTik] /system health> print
fan-mode: auto
use-fan: main
active-fan: main
voltage: 14
[admin@MikroTik] /system health>
The voltage follows the battery charger voltage display.
Are you using the power input or PoE? Mine is on the power input.
On ROS V3.10 and below, it had no voltage monitor.