All 5 devices suddenly reports below 5% battery left and all become unavailable

[ClausDK]

Over one day, all my 5 devices (3 Arlo, 2 Arlo Pro) connected to the same base station report low battery. Not just below 20%, but zero. This means that they are now unavailable. My system has been running OK in this configuration for a 18-24 months with no changes. I check the system every 2nd or 3rd day and and the camera with the low capacity was only around some 40%.. 

[TomMac]

Easy thing to do is power reboot the base... test