Batteries not holding charge

I wonder if anyone can help, I have the ring doorbell 2 (battery powered). I have two batteries which I alternate, but this last week, nether battery seems to charge. As soon as I replace the battery it’s shows as offline/dead battery. The charging light comes on on the battery when the charger is connected but it still shows dead when changed. If it was just one I’d think faulty battery maybe but it seems strange that it’s both. Thanks in advance 😊