I don't use my camera too often. Sometimes it can be a month or two in between use. Yesterday I decided to use my DSLR instead of my phone. When I turned it on, the battery was low and ERR was flashing on the LCD screen. I figured it was because the battery was low and I haven't used the camera in a while. I went ahead and fully charged the battery, turned the camera on again and this time no ERR flashing. Great, right? Well not so fast. I took a shot and the ERR started to flash after taking a picture. Flash popped up and the picture actually came out great. I took a few more shots and the ERR would flash after each time I took a picture. I tried switching out the SD card, used two other batteries and also switched out the 18-55mm lens for a Macro lens. Still, the ERR would flash after each shot. About 15 minutes of messing with it, suddenly the ERR stopped flashing after taking pictures. I was thinking maybe the internal cmos battery was low and it took time for it to charge up from a fully charged battery? Or is something going bad in my camera? Anyone had such experience?
CMOS battery or supercapacitor charging are likely culprits, as you state. Keep the battery charged to prevent losing date/time and customized settings, as well.