FGT60F and FortiWiFi-60F - Time is Wrong After Power Loss

Hello, 

Recently, within one week of one another, had a FGT60F and a FortiWiFi-60F boot with incorrect time and date after an unexpected and more than one hour power loss. Year was 1999 once and 2000 on the other device.

Both devices are running firmware v7.4.11 build 2878 and connected to FortiGate cloud with valid subscriptions.

After the power loss, local traffic is not able to communication with Fortiguard DNS due to the time issue. Therefore:

Updating time via Fortiguard NTP servers fails.

Fortilink devices show as offline.

Fortigate Cloud MGMT down.

Having to update devices to use 8.8.8.8, 8.8.4.4 for system DNS. NTP then updates using FortiGuard and after some time, FortiGuard DNS will allow communication again. 

One device is 3 years old and the other is around 5. 
Checked for a way to check the internal battery status but came up empty. 

Any help or thoughts are appreciated.