Full battery shows no charge on one side only

We've had our spotlight cam for 18 months and really like it. However, starting this morning, when I go to Devices and then select the camera, it shows that the left battery is totally drained, even when I've replaced it with a fully charged one. I tried swapping out the two batteries (right battery into left slot and vice versa) and it still shows that the left side has a drained battery. Any suggestions on how to fix this? TIA!