Video Doorbell Pro slow charging

Our Video Doorbell Pro (VDP) has been installed for almost 9 months since we got it and fully charged it to 100%. Recently it got down to single digits of reported charge and so I removed it off the mount o charge it.

After charging it overnight, it was only reporting a 30% charge. Not to impact our customers coming to our office and letting us know they are here, I reinstalled. Two months later, it is low again and again I when to charge it and left it for 20 hours to only get 32% reported charge.

Is this normal? Any ideas what might be going on here?