With BTT 6.021 you can query the Battery State via BTT's Java Script. Here is an example that gets the battery state and saves it to variable "mxmaster_battery":
async function getLogitechBattery() {
const result = await logitech_get_battery_status({ deviceName: "MX Master" });
await set_number_variable({variableName: "mxmaster_battery", to: result.level});
return result;
}
You can then use that variable however you like, for example this preset shows a HUD with the battery state when pressing ctrl+opt+cmd+D:
logitech_battery.bttpreset (3.7 KB)
You could also have a time based trigger that checks e.g. once per hour and uses an if condition to check whether the battery is below a specific percentage - and only then shows the HUD.