That's my best guess. If the camera has a battery (or a large enough capacitor), if the power goes out or during the ring event when the voltage/current drops, the camera can continue to operate as normal through the backup power source. If the batteries are rechargeable, then the camera would never need to be removed from the wall. I personally prefer either lithium rechargeable batteries or better yet a large capacitor.
The Blink camera has no local storage inside the device. It does have 2 versions on the shelf: 1) camera, 2) camera + local sync adapter. The sync adapter is basically a plugin device that appears to have a plug for a USB device so you can set up storage from the camera(s). I have read that it does work but is very clunky in it's implementation. Also (and more importantly) it does not have RTSP so there is no way to connect the camera to other systems. I plan to use my Synology NAS to provide local storage. It is compatible with many camera types and allows for a generic RTSP if it is not listed (Blink is not listed but does not have RTSP either apparently).
For something that I thought would be simple, the list of requirements seems to be getting longer:
- Wired/wireless power
- Works with existing chimes
- Local storage
- RTSP support
- No subscription requirement
- Supports up to 3 cameras
- Can't cost a fortune (I want 3 so that would add up quickly)
I looked at some other options last night though it is difficult to narrow down with my ridiculous requirement list. It looks like one camera that might work is the Eufy S220. I'll have to do more looking but it appears that it is wired/wireless, local storage, RTSP, no subscription, and on sale for $90USD. They seem to have a large user community so that is a nice bonus. I'll check if they have a discord to ask detailed questions.
https://us.eufy.com/products/e82101w3