headsetcontrol-battery-widget/package/contents/ui/lib/helper.js

const colors = [
  '#f00', '#e21c00', '#c83800', '#a50', '#8d7100',
  '#718d00', '#6fa100', '#5c8000', '#498000', '#080'
];

const batteryColor = batteryPercent => colors[({
  "-2": 9,
  "-1": 0
})[batteryPercent] ?? ~~(batteryPercent / 10 + 0.5) - 1];

const batteryLevel = batteryPercent => ({
  "-2": "not connected",
  "-1": "charging"
})[batteryPercent] ?? batteryPercent + "%";

const batteryIcon = batteryPercent => ({
  "-2": "action-unavailable",
  "-1": "battery-ac-adapter"
})[batteryPercent] ?? "audio-headphones-symbolic";