--- title: "Battery, not processor: how long a deck runs off the grid" url: "https://kyberdeck.com/blog/battery-not-processor" description: "For a device you carry, the real limit is energy per task, not peak compute. What drains a deck, which design choices save it, and how you see the trade-off yourself." --- # Battery, not processor: how long a deck runs off the grid October 20, 2026·4 min read·Editorial team A wrist unit on its strap beside a flat pouch battery, with a small analogue meter whose needle sits close to empty A site engineer spends the morning walking a half-built warehouse with a wrist unit on. She asks it short things: which bay is next, what the fitter said yesterday about the cable tray, remind me at the gate. Around lunch the unit goes quiet. Not broken, just empty. The nearest socket is in a portacabin on the other side of the yard. For the rest of the day she takes notes on paper. The assistant that was supposed to be with her all day was with her until lunch. Nobody asked that device to be fast. They asked it to last. The spec sheet talked about the processor. ## The real cause: a carried device is an energy budget A phone or a laptop is judged by what it can do at full tilt. A device that lives on your wrist or your lanyard is judged by how many tasks it can do before it stops. That is a different number. It is energy per task multiplied by the number of tasks you ask for, against a battery that has to fit in something small enough to forget you are wearing it. Peak compute only tells you how fast the budget can be spent. ## Where the energy actually goes **Listening all the time.** An assistant that waits for your voice has a microphone chain and some kind of detector running every second, including the hours when nobody says anything. If that detector is a general model, it is the most expensive thing on the device, and it is on all day. **Radios looking for something to talk to.** Wi-Fi scanning, a cellular modem hunting for a cell at the edge of coverage, Bluetooth keeping a link warm: each one is a steady drain that has nothing to do with your request. Out of coverage, the modem searching is often the single biggest cost. **Models larger than the task.** Answering “which bay is next” with a model sized for writing essays burns the energy of an essay. The time to the answer is what you notice; the charge it took is what you pay for later. **Screens that stay bright.** A display that lights up on every notification and stays on in case you glance at it spends charge on your attention, not your work. **Waking up for every little thing.** Each wake from deep sleep costs more than the work that follows. A device that wakes ten times to do ten small jobs spends more than one that wakes once and does them together. **Sync that cannot wait.** Pushing every note home the moment it exists means the radio is never allowed to rest. ## What a deck does with that budget The constraint cannot be designed away. It can be spent well. These are the choices KyberDeck is designed around, and all of them are design targets rather than measured results. **A tiny model guards the door.** The always-on part is the smallest thing that can reliably hear a wake word. Nothing larger runs until that small model says there is something worth running for. A carried device does not need the large model to be awake; it needs the large model to be reachable. **Work is batched.** Notes, transcriptions and sync are queued and done in one wake rather than many. The device spends more time asleep and less time half-awake. **Heavy work leaves the wrist.** The band and the card carry the day; anything bigger goes to the pocket deck or to [the home node](https://kyberdeck.com/blog/the-home-node), which is plugged into a wall and does not care about any of this. KyberBot decides where a job runs, and the energy cost of running it here is part of that decision. This is also why [small models are enough](https://kyberdeck.com/blog/small-models-are-enough) for the near-you work. **Radios rest by default.** Offline is a normal state, not a failure. Sync waits until there is something to sync to and the device is not busy keeping itself alive. **The switch is physical.** A hardware mute does not only protect you from being heard. It also stops the listening chain from drawing anything at all. **The trade-off is yours to see.** Battery settings on most devices are a single slider called “performance” that nobody understands. The design goal here is plainer: show what each behaviour costs, in the device’s own terms, and let you turn it down. Listen for the wake word only when the band is raised. Keep the modem asleep until you are home. Answer from the small model unless you ask for more. Each of those is a trade you can make, and the device should tell you what you got for it. What it does not do: it does not run the largest models on the device, and no battery will make that a good idea. It does not promise a number of hours, because there is no unit yet to measure one on. ## A test you can run today Take the device you carry now and look at its battery usage screen for the past day. Most systems list consumption per app or per subsystem. Write down the top three entries, and next to each one write down how many times you actually asked that thing to do something. Then do a second day with the always-on assistant features switched off: no voice wake, no background listening, radios allowed to sleep. Compare. If the top consumers were things you never asked for, you have found the real constraint. The processor was never the limit. The budget was, and nobody showed you where it went. That is the whole argument for a carried device designed around energy per task rather than peak speed, and it is the argument behind every form on [the KyberDeck homepage](https://kyberdeck.com/). The other reason a carried device should hold less than you think is in [what a stranger can read from a lost deck](https://kyberdeck.com/blog/a-lost-deck). - battery - power budget - on-device - KyberDeck Band - KyberDeck Node ## Keep reading - [A lost deck: what a stranger can read from it](https://kyberdeck.com/blog/a-lost-deck) - [Android XR and who owns the body of your assistant](https://kyberdeck.com/blog/android-xr-and-who-owns-the-body)