Video Doorbell Pro Voltage Dropping?

Hello, I installed my DB Pro a little over a week ago. I have no existing doorbell wiring, so I bought the below 26 ft transformer off Amazon. I needed the extra length as the Ring adapter is not long enough. It's a 24 Volt power supply, and I measured it with a multimeter to see that it's supplying the correct voltage, which it is. I'm not having any issues whatsoever with my DB Pro, and experience no symptoms of insufficient power--it's working absolutely perfectly. The 'Doorbell Kit' in the app is correctly set to 'None.' However, when first installed a little over a week ago, my voltage was well above 4,000 mV. The voltage continues to drop by 8 or so mV each day, and I'm currently down to 3,938 mV. Is this normal? Will it reach a certain point, then recharge the internal battery? I'm worried I may eventually experience power issues once this drops low enough, and am trying to proactively address this before I have problems. Thanks much! [https://www.amazon.com/gp/product/B07DJ7RHS5/ref=ppx\_yo\_dt\_b\_asin\_title\_o08\_s00?ie=UTF8&psc=1](https://www.amazon.com/gp/product/B07DJ7RHS5/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1)