I haven't developed on the Kindle ecosystem, but with old Nook devices I am able to set a screensaver, alarm, and put the device into deep sleep between refreshes. This changed my battery life from ~48 hours into 30+ days of battery life even with some old devices.

The "electric sign" app does this, which is where I referenced the code.

With trmnl, the image only refreshes every 10 mins so the device will set a ~9 minute alarm to wake the device right before it needs to load the next update.

The refresh period is also configurable so a slower refresh interval (e.g. every hour for less time-sensitive screens) yields larger battery savings

I removed the battery but kept the I2C chip/pcb, and fed 5V from USB port via a diode, on the PCB battery connections, seems to work fine. I actually installed a single wire from USB VCC to diode then + battery terminal. But you need to power the Kindle from something that can deliver at least 1.5A for startup peaks. A USB hub does the job fine in my case, and also connects it to a raspberry pi for ssh through USB networking, so no wifi either. Use a good USB cable for power.

Yeah that was definitely a worry of mine before I booted it up. Luckily it's still got decent battery life. We'll see how it holds up in 6 months...

Dyson vacuums and Kindles are not the same whatsoever, but I wonder how easily it'd be to swap out the battery on an older Kindle. For our vacuum, all I needed was a 20 dollar replacement battery and the will unscrew 3 mini screws.

One thing that's disappointed me is that despite all the excitement over better and cheaper battery technology, you can't buy a cheapish drop in replacement battery for e.g. an old kindle that has more storage capacity than the OEM version.

I understand there's like all sorts of complexities in standards, form factors, voltage, wattage, etc, but I really wish I could upgrade my old devices like that.