A quarter of a milliamp-hour can still do useful work
The battery shown in BTRY’s recent presentation held 0.25mAh. That is a small number even by the standards of miniature electronics. Its other number was more revealing: a peak current of 10mA, enough for short Bluetooth Low Energy transmissions.
Capacity and power describe different jobs. Capacity sets the amount of charge available; peak current describes how quickly it can be delivered. A device that sleeps for long periods and briefly wakes its radio may need very little total energy during each transmission, while still asking for a substantial current relative to the size of its cell.
As a simple calculation, 0.25mAh divided by a continuous 10mA load gives 0.025 hours, or 90 seconds. That is an ideal arithmetic ratio, not a runtime measured by BTRY. It ignores voltage limits, pulse behaviour, conversion losses and the way usable capacity changes with operating conditions. What it illustrates is why this cell belongs in a discussion about intermittent loads rather than continuous radio operation.
Building the battery in layers
BTRY manufactures thin-film solid-state cells using vacuum-deposition methods adapted from semiconductor and related production processes. Its technology programme began with small proof-of-concept cells at Empa, progressed to flexible metal foil and subsequently reached an industrial production line.
The manufacturing approach is part of the appeal. Thin layers shorten the distances involved in the cell structure, while stacked cells offer a route towards more stored energy. Stacking also adds material, connections and manufacturing steps, so increasing capacity has consequences for the package and the process used to make it.
The company reports charging and discharging on approximately a one-minute timescale and has demonstrated high-temperature operation. Those descriptions apply to the technology and particular test articles; the ratings of a selected product still have to come from its own specification. A demonstration at 150°C does not automatically establish the operating range of every BTRY cell.
The combination is relevant to objects that have very little room for a battery: a label, a compact sensor or a device that gathers small amounts of energy between short periods of activity. In an energy-harvesting system, the cell can provide a store from which a radio draws a pulse, even when the harvester cannot supply that instantaneous current itself.
BTRY is also working with InsightSilica on batteries for the semiconductor industry. The companies describe development work combining a compact energy store with demanding thermal environments, rather than a finished replacement for every conventional battery chemistry.
