Here are the parts I bought, I'm still getting it all setup (I have my pictures displaying, working on designing the 3D printed case now, and testing it all) but according to OpenDisplay's calculator [0] I can expect 3.4 years if I refresh the screen once every 4 hours (and currently I'm doing closer to once a day to mimic my ESP32s which need deep sleep and once-a-day refresh to get even month/months of battery on a charge).
Screen: 7.5" Monochrome eInk / ePaper Display with 800x480 Pixels (https://www.seeedstudio.com/7-5-Monochrome-ePaper-Display-wi...)
BTLE board: XIAO ePaper Display Board(nRF52840) - EN05 (https://www.seeedstudio.com/XIAO-ePaper-Display-Board-nRF528...)
Battery: 3.7V 2000mAh - (https://www.amazon.com/dp/B0FR9GH966)
Picture of it all assembled (no case yet): https://cs.joshstrange.com/zJFvGGPB
The image rendered to the screen is coming from a little service I wrote that renders a book quote it pulls from BookOrbit which syncs with KOReader (annotations, progress, etc). My plan is to set up one of these one each bookshelf/series rotating quotes I highlighted from the series.
Here are 2 ESP32-based screens I have, the one on the left is a an all-in-one [1] and the one on the right I printed the case from the TRMNL DIY kit from SeeedStudio [2]: https://cs.joshstrange.com/knk4Ns2h
Right now only the BTLE one is running OpenDisplay (the other two are semi-managed by HomeAssistant ESPHome) and all the devices are in HA for controlling them, though the ESP32's all deep-sleep for saving battery so I can can't "push" stuff to them like I can the BTLE one.
[0] https://opendisplay.org/index.html#battery
[1] https://www.seeedstudio.com/reTerminal-E1001-p-6534.html
[2] https://www.seeedstudio.com/TRMNL-7-5-Inch-OG-DIY-Kit-p-6481...
If I want a wifi e-ink connected display - curious what would you recommend. I want an e-ink display - that I can use as a sign/display board with wifi connectivity and remote administration.
If you want a simple e-ink wifi screen I'd point you at the reTerminal e1001 [0] if that size works for you. It's the easiest to get started with. You can either keep it on power or use the deep sleep to get more from the battery. It really comes down to how often you want to update it.
The BTLE boards have just crazy higher battery time with no need for deep sleep which is why I'm moving in that direction.
~7.5" is the size I've been buying so far, the larger e-ink screens get pricey but I can't wait for a calendar-sized one to come down in price such that I can frame it and hang it on the wall. Lastly I'd avoid the color e-ink screens unless you know you need color, won't need to refresh it often, and it's not in your eye line. Color refreshes take way longer (~30s in my experience for a 5-6 color screen) and the flashing it has to do is obnoxious. Monocolor displays take <2s normally and a single flash. I got a color screen first because "why not?" and I got color, but the refresh was too annoying so now it refreshes once a day in a place that I'm not when it refreshes so I don't have to see it.
I also recommend you check out OpenDisplay for what you will run on the device: https://opendisplay.org/index.html
[0] https://www.seeedstudio.com/reTerminal-E1001-p-6534.html