This means your battery voltage is too low. Replacing the station battery with a fully charged one and soft rebooting the unit should fix the problem. In the station screen menu, go to Tools > Reboot > Yes to execute a soft reboot. You will not lose any data.
If you don’t have an extra battery to use in place of the low voltage battery, it takes about 11 hours to charge a dead FieldKit battery, so you will need to either:
Turn the station off and let it charge. You can do this via solar if you have a solar setup. Come back in a day and turn it back on.
Remove the battery, bring it back with you, and charge it using an external charger. Then replace it later.
In either case, keep an eye on the battery voltage in the future. If power becomes a consistent issue, you may want to consider adding a solar panel if you aren’t using one, or adjusting your current solar panel implementation.