LightInk solar E Ink watch claims around 400 days of battery life

LightInk is an open-source DIY solar E Ink watch that pushes battery life to an extreme. It is built around an ESP32, a small solar cell and custom low-power hardware, with the aim of making a basic watch that can run for months, or potentially keep itself topped up from light.

The device feels like a throwback to the original Pebble era, when smartwatch design was still more about practicality than loading a wrist with apps and sensors. The focus here is simple: an always-visible E Ink display, extremely low power draw and a watch that tries to avoid the charger for as long as possible.

The trick is cutting everything back

The project is based on the same broad idea as Watchy, the open source E Paper watch platform. The difference is that LightInk goes much harder on power optimisation, using specific hardware choices to reduce the small background drains that usually make ESP32 wearables difficult for long battery life.

The headline claim is around 2uA consumption when the watch is just updating the time. With a 200mAh battery, similar to Watchy, the developer estimates roughly 400 days of battery life before solar top-ups are even counted. The project target is below 0.5mAh per day, which is the sort of number that makes normal smartwatch charging cycles look a bit silly.

LightInk uses a TPS63900 power setup with selectable 2.6V and 2.9V output, enough to power the ESP32, RTC, E Ink display and WiFi when needed. It also drops the accelerometer, because even when disabled it reportedly consumes around 1uA. On most watches that would barely register. Here, it is big enough to remove.

There are still some smart features

This is not just a solar clock with a strap. LightInk includes capacitive touch instead of buttons, a piezo speaker, vibration, an LED light for viewing the screen in the dark, WiFi time sync, alarms, battery tracking and power saving modes.

LoRa and GPS support are also listed, but these are clearly occasional-use tools rather than always-on features. Treat GPS like you would on a sports watch and the 400-day battery story falls apart very quickly. That does not make the claim useless, but it does show what kind of device this really is.

The battery figure only works because LightInk spends most of its life doing very little. E Ink helps because it mainly consumes power when the screen updates, not while the image sits there. The project also avoids showing seconds, because refreshing the display every second would defeat the whole point.

It looks rough because it is built for function

The design will split people. The current version has a blocky case, a visible solar strip and a layout that looks closer to an electronic shelf label than a polished smartwatch. A solar rim or cleaner case would probably look better, but that would also move the project away from the practical off-the-shelf approach that makes it possible.

That roughness might actually be part of the appeal. LightInk is not trying to be an Apple Watch alternative, a Garmin rival or even a Pebble replacement in any normal sense. It is a maker project that asks how much battery life you can squeeze from E Ink, solar, careful firmware work and ruthless hardware choices.

The solar claim also needs context. If the watch keeps topping itself up from light, then “single charge” is not quite the same as running untouched in a drawer for more than a year. The more useful way to read it is that the baseline power draw is low enough for a small solar cell to make a real difference.

A useful reminder for wearables

LightInk probably will not become a mass-market product in this form. The project itself notes that building a unit requires a lot of soldering, and the plan is mainly to keep developing and fixing a personal unit. That makes sense. This is open-source maker hardware, not something most buyers will assemble over a weekend.

Still, the project is a neat reminder that wearable design does not always have to mean brighter screens, more sensors and shorter battery life. Strip away the constant background drains, use E Ink properly and make solar part of the core design. Suddenly, a watch that can run for months does not sound so strange.

Source: Github via NotebookCheck