diff --git a/internal/profile/detectors.go b/internal/profile/detectors.go
index 7e76af6..604f49d 100644
--- a/internal/profile/detectors.go
+++ b/internal/profile/detectors.go
@@ -187,6 +187,8 @@ func Default(runner Runner) []Detector {
 		privileged{},
 		graphicalSession{},
 		seat{},
+		battery{},
+		powerMeter{},
 		commandCapability{
 			name: CapContainerRuntime, command: "docker", args: []string{"info", "--format", "{{.ServerVersion}}"},
 			why:    "asks the daemon for its version — a running daemon, not an installed client",
diff --git a/internal/profile/power.go b/internal/profile/power.go
new file mode 100644
index 0000000..48efcc6
--- /dev/null
+++ b/internal/profile/power.go
@@ -0,0 +1,135 @@
+package profile
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// What this machine has to say about its own power (novox/hq ADR 0255): whether it has a battery,
+// and whether anything on it can measure the power it draws.
+//
+// **Hardware, read from the kernel, as `seat` is.** A module that shows a battery, or the power a
+// machine draws, is on every machine — the power module holds node-power everywhere — and what it
+// shows depends on what is there. The controller composes such a piece only where the machine
+// reported the capability, so a desktop never gets a battery block that would sit empty, and the
+// bar never asks at run time what the mesh could have said once.
+
+// Named power capabilities.
+const (
+	// CapBattery is a battery that powers this machine: a power supply of type Battery that is not
+	// a device's (a mouse's or a headset's battery has scope Device).
+	CapBattery = "battery"
+	// CapPowerMeter is something here that measures the power the machine, or part of it, draws:
+	// the machine's battery, the processor package's energy counter (powercap, Intel's and AMD's
+	// RAPL), or a discrete graphics device that reports its own power — the same meters the power
+	// module's sampler reads, so a machine never gets a block that can only say "not measured".
+	CapPowerMeter = "power-meter"
+)
+
+// Where the kernel reports supplies and energy counters. Variables so a test can point them at a
+// directory it made, rather than at whatever this machine happens to have.
+var (
+	PowerSupplySource = "/sys/class/power_supply"
+	PowercapSource    = "/sys/class/powercap"
+	NvidiaSource      = "/proc/driver/nvidia/gpus"
+)
+
+// systemBatteries is every battery that powers this machine, by name.
+func systemBatteries() []string {
+	entries, err := os.ReadDir(PowerSupplySource)
+	if err != nil {
+		return nil
+	}
+	var out []string
+	for _, e := range entries {
+		dir := filepath.Join(PowerSupplySource, e.Name())
+		if readTrimmed(filepath.Join(dir, "type")) != "Battery" {
+			continue
+		}
+		if readTrimmed(filepath.Join(dir, "scope")) == "Device" {
+			continue
+		}
+		// A bay with no battery in it still has a directory.
+		if readTrimmed(filepath.Join(dir, "present")) == "0" {
+			continue
+		}
+		out = append(out, e.Name())
+	}
+	sort.Strings(out)
+	return out
+}
+
+func readTrimmed(path string) string {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(b))
+}
+
+type battery struct{}
+
+func (battery) Name() string { return CapBattery }
+
+func (battery) Detect(context.Context) Verdict {
+	const how = "/sys/class/power_supply/*/type — a Battery whose scope is not Device"
+	if found := systemBatteries(); len(found) > 0 {
+		return Verdict{Name: CapBattery, Present: true, Detail: strings.Join(found, ", "), How: how}
+	}
+	return Verdict{Name: CapBattery, Present: false, Detail: "no battery powers this machine", How: how}
+}
+
+type powerMeter struct{}
+
+func (powerMeter) Name() string { return CapPowerMeter }
+
+// Detect names every meter it found. Only that one exists: whether its counter can be read is the
+// reader's question — powercap's energy counter is root's to read, and the power module samples it
+// as root and publishes only a rate.
+func (powerMeter) Detect(context.Context) Verdict {
+	const how = "a system battery; /sys/class/powercap/*/name starting package, each name once; a discrete " +
+		"graphics device's (mem_info_vram_vendor) hwmon power1_average or power1_input; /proc/driver/nvidia/gpus"
+	var found []string
+	for _, b := range systemBatteries() {
+		found = append(found, "battery "+b)
+	}
+	// Each package once by its name: Intel shows some twice, as intel-rapl:N and intel-rapl-mmio:N.
+	if entries, err := os.ReadDir(PowercapSource); err == nil {
+		seen := map[string]bool{}
+		for _, e := range entries {
+			dir := filepath.Join(PowercapSource, e.Name())
+			name := readTrimmed(filepath.Join(dir, "name"))
+			if !strings.HasPrefix(name, "package") || seen[name] {
+				continue
+			}
+			if _, err := os.Stat(filepath.Join(dir, "energy_uj")); err == nil {
+				seen[name] = true
+				found = append(found, "processor "+name)
+			}
+		}
+	}
+	if cards, err := filepath.Glob(filepath.Join(SeatSource, "card*", "device", "hwmon", "hwmon*")); err == nil {
+		for _, hw := range cards {
+			// Integrated graphics report the package the processor's counter already holds.
+			if _, err := os.Stat(filepath.Join(filepath.Dir(filepath.Dir(hw)), "mem_info_vram_vendor")); err != nil {
+				continue
+			}
+			for _, f := range []string{"power1_average", "power1_input"} {
+				if _, err := os.Stat(filepath.Join(hw, f)); err == nil {
+					found = append(found, "graphics "+strings.Split(strings.TrimPrefix(hw, SeatSource+"/"), "/")[0])
+					break
+				}
+			}
+		}
+	}
+	if gpus, err := os.ReadDir(NvidiaSource); err == nil && len(gpus) > 0 {
+		found = append(found, "graphics nvidia")
+	}
+	if len(found) == 0 {
+		return Verdict{Name: CapPowerMeter, Present: false, Detail: "nothing here measures the power drawn", How: how}
+	}
+	return Verdict{Name: CapPowerMeter, Present: true, Detail: strings.Join(found, ", "), How: how}
+}
diff --git a/internal/profile/power_test.go b/internal/profile/power_test.go
new file mode 100644
index 0000000..aebea24
--- /dev/null
+++ b/internal/profile/power_test.go
@@ -0,0 +1,133 @@
+package profile
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// Defends novox/hq ADR 0255: a machine says whether a battery powers it and whether anything on it
+// measures the power it draws, read from the kernel, so the controller composes a battery's or a power
+// draw's block only where there is one.
+
+func write(t *testing.T, path, content string) {
+	t.Helper()
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte(content+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// sysfs points every power source at a directory of its own, empty unless a case fills it.
+func sysfs(t *testing.T) string {
+	t.Helper()
+	dir := t.TempDir()
+	old := [4]string{PowerSupplySource, PowercapSource, SeatSource, NvidiaSource}
+	PowerSupplySource = filepath.Join(dir, "power_supply")
+	PowercapSource = filepath.Join(dir, "powercap")
+	SeatSource = filepath.Join(dir, "drm")
+	NvidiaSource = filepath.Join(dir, "nvidia")
+	t.Cleanup(func() { PowerSupplySource, PowercapSource, SeatSource, NvidiaSource = old[0], old[1], old[2], old[3] })
+	return dir
+}
+
+func TestALaptopHasABatteryAndAMeter(t *testing.T) {
+	dir := sysfs(t)
+	write(t, dir+"/power_supply/ACAD/type", "Mains")
+	write(t, dir+"/power_supply/BAT1/type", "Battery")
+	write(t, dir+"/power_supply/BAT1/scope", "System")
+	write(t, dir+"/power_supply/BAT1/present", "1")
+	write(t, dir+"/powercap/intel-rapl:0/name", "package-0")
+	write(t, dir+"/powercap/intel-rapl:0/energy_uj", "1")
+
+	b := battery{}.Detect(context.Background())
+	if !b.Present || b.Detail != "BAT1" {
+		t.Fatalf("battery: %+v", b)
+	}
+	m := powerMeter{}.Detect(context.Background())
+	if !m.Present || m.Detail != "battery BAT1, processor package-0" {
+		t.Fatalf("power meter: %+v", m)
+	}
+}
+
+func TestADevicesBatteryIsNotTheMachines(t *testing.T) {
+	// The case worth a test: a desktop with a wireless mouse reports a Battery, and a battery block
+	// composed for it would show the mouse's charge as the machine's.
+	dir := sysfs(t)
+	write(t, dir+"/power_supply/hidpp_battery_0/type", "Battery")
+	write(t, dir+"/power_supply/hidpp_battery_0/scope", "Device")
+	write(t, dir+"/power_supply/BAT0/type", "Battery")
+	write(t, dir+"/power_supply/BAT0/present", "0")
+
+	if b := (battery{}).Detect(context.Background()); b.Present {
+		t.Fatalf("a mouse's battery, or an empty bay, was taken for the machine's: %+v", b)
+	}
+	if m := (powerMeter{}).Detect(context.Background()); m.Present {
+		t.Fatalf("a device's battery was taken for a meter: %+v", m)
+	}
+}
+
+func TestADesktopMeasuresItsProcessorAndItsGraphics(t *testing.T) {
+	dir := sysfs(t)
+	write(t, dir+"/powercap/intel-rapl:0/name", "package-0")
+	write(t, dir+"/powercap/intel-rapl:0/energy_uj", "1")
+	// A sub-domain is part of the package, not a second meter.
+	write(t, dir+"/powercap/intel-rapl:0:0/name", "core")
+	write(t, dir+"/powercap/intel-rapl:0:0/energy_uj", "1")
+	write(t, dir+"/drm/card1/device/hwmon/hwmon4/power1_average", "8000000")
+	write(t, dir+"/drm/card1/device/mem_info_vram_vendor", "samsung")
+	write(t, dir+"/nvidia/0000:01:00.0/information", "x")
+
+	if b := (battery{}).Detect(context.Background()); b.Present {
+		t.Fatalf("a desktop has a battery: %+v", b)
+	}
+	m := powerMeter{}.Detect(context.Background())
+	if !m.Present || m.Detail != "processor package-0, graphics card1, graphics nvidia" {
+		t.Fatalf("power meter: %+v", m)
+	}
+}
+
+func TestAMachineWithNothingToReadHasNeither(t *testing.T) {
+	sysfs(t)
+	b, m := battery{}.Detect(context.Background()), powerMeter{}.Detect(context.Background())
+	if b.Present || m.Present || b.How == "" || m.How == "" || !strings.Contains(m.Detail, "nothing") {
+		t.Fatalf("%+v %+v", b, m)
+	}
+}
+
+func TestAPackageShownTwiceIsOneMeterAndIntegratedGraphicsAreNone(t *testing.T) {
+	dir := sysfs(t)
+	write(t, dir+"/powercap/intel-rapl:0/name", "package-0")
+	write(t, dir+"/powercap/intel-rapl:0/energy_uj", "1")
+	write(t, dir+"/powercap/intel-rapl-mmio:0/name", "package-0")
+	write(t, dir+"/powercap/intel-rapl-mmio:0/energy_uj", "1")
+	// An APU's graphics: power reported, no memory of its own.
+	write(t, dir+"/drm/card1/device/hwmon/hwmon5/power1_average", "19000000")
+	m := powerMeter{}.Detect(context.Background())
+	if !m.Present || m.Detail != "processor package-0" {
+		t.Fatalf("power meter: %+v", m)
+	}
+}
+
+func TestOnlyIntegratedGraphicsMeasureNothing(t *testing.T) {
+	dir := sysfs(t)
+	write(t, dir+"/drm/card0/device/hwmon/hwmon1/power1_input", "5000000")
+	if m := (powerMeter{}).Detect(context.Background()); m.Present {
+		t.Fatalf("integrated graphics were taken for a meter: %+v", m)
+	}
+}
+
+func TestABatteryOfUnknownScopeIsTheMachines(t *testing.T) {
+	// Many laptops' firmware says nothing of scope; the kernel reports Unknown. Only Device is a
+	// peripheral's.
+	dir := sysfs(t)
+	write(t, dir+"/power_supply/BAT0/type", "Battery")
+	write(t, dir+"/power_supply/BAT0/scope", "Unknown")
+	if b := (battery{}).Detect(context.Background()); !b.Present || b.Detail != "BAT0" {
+		t.Fatalf("battery: %+v", b)
+	}
+}