diff --git a/app/src/main/java/com/droiddeck/launcher/session/BatteryComponent.kt b/app/src/main/java/com/droiddeck/launcher/session/BatteryComponent.kt
index 9b0834e17..fc6526f59 100644
--- a/app/src/main/java/com/droiddeck/launcher/session/BatteryComponent.kt
+++ b/app/src/main/java/com/droiddeck/launcher/session/BatteryComponent.kt
@@ -14,7 +14,7 @@ import kotlin.math.abs
  * The client reads `/sys/class/power_supply/BAT<n>/...` - a laptop's or a Deck's naming and files
  * (`energy_now`, `power_now`, `time_to_empty_now`, a `uevent` of `POWER_SUPPLY_*` lines). Android
  * names its supply `battery` and lays it out differently, and on many phones an app may not read
- * it at all, so the client showed no battery. This writes a `BAT0` (and a `BAT1`, the Deck's name)
+ * it at all, so the client showed no battery. This writes one `BAT1` (the Deck's name)
  * from Android's own battery API - the same on every device - into a directory the session binds
  * over `/sys/class/power_supply`, refreshed every few seconds while the session runs.
  *
@@ -31,6 +31,8 @@ class BatteryComponent(val dir: File, private val vpowerDir: File) : SessionPart
     private var thread: Thread? = null
 
     override fun start() {
+        // Older builds exported the same aggregate battery twice; MangoHud counts both supplies.
+        File(dir, "BAT0").deleteRecursively()
         running = true
         write()
         thread = Thread({
@@ -39,7 +41,7 @@ class BatteryComponent(val dir: File, private val vpowerDir: File) : SessionPart
                 if (running) write()
             }
         }, "battery-sysfs").apply { isDaemon = true; start() }
-        Log.i(TAG, "battery: BAT0/BAT1 written to ${dir.path} every ${PERIOD_MS / 1000} s")
+        Log.i(TAG, "battery: BAT1 written to ${dir.path} every ${PERIOD_MS / 1000} s")
     }
 
     override fun stop() {
@@ -87,7 +89,7 @@ class BatteryComponent(val dir: File, private val vpowerDir: File) : SessionPart
                 pct <= 15 -> "Low"
                 else -> "Normal"
             }
-            for (name in listOf("BAT0", "BAT1")) {
+            for (name in listOf("BAT1")) {
                 val bat = File(dir, name).apply { mkdirs() }
                 val attrs = linkedMapOf(
                     "type" to "Battery",
diff --git a/app/src/test/java/com/droiddeck/launcher/session/BatteryComponentTest.kt b/app/src/test/java/com/droiddeck/launcher/session/BatteryComponentTest.kt
new file mode 100644
index 000000000..fd820e22b
--- /dev/null
+++ b/app/src/test/java/com/droiddeck/launcher/session/BatteryComponentTest.kt
@@ -0,0 +1,71 @@
+package com.droiddeck.launcher.session
+
+import android.content.Intent
+import android.os.BatteryManager
+import java.io.File
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Rule
+import org.junit.Test
+import org.junit.rules.TemporaryFolder
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+import org.robolectric.Shadows.shadowOf
+import org.robolectric.annotation.Config
+
+@RunWith(RobolectricTestRunner::class)
+@Config(sdk = [28], manifest = Config.NONE)
+class BatteryComponentTest {
+    @get:Rule val tmp = TemporaryFolder()
+    private var battery: BatteryComponent? = null
+
+    @After fun stop() { battery?.stop() }
+
+    @Test fun oneAggregateBatteryKeepsOverlayPowerAndLifetimeConsistentWithQam() {
+        val supplies = tmp.newFolder("power_supply")
+        val vpower = tmp.newFolder("vpower")
+        start(supplies, vpower, -2_000_000L)
+        assertTelemetry(supplies, vpower)
+    }
+
+    @Test fun upgradingRemovesTheDuplicateRatherThanLeavingItForOverlayDiscovery() {
+        val supplies = tmp.newFolder("power_supply")
+        val vpower = tmp.newFolder("vpower")
+        val legacy = File(supplies, "BAT0").apply { mkdirs() }
+        File(legacy, "power_now").writeText("8000000\n")
+        File(legacy, "charge_now").writeText("4000000\n")
+        start(supplies, vpower, 2_000_000L)
+        assertFalse(legacy.exists())
+        assertTelemetry(supplies, vpower)
+    }
+
+    private fun start(supplies: File, vpower: File, currentUa: Long) {
+        val context = RuntimeEnvironment.getApplication()
+        context.sendStickyBroadcast(Intent(Intent.ACTION_BATTERY_CHANGED).apply {
+            putExtra(BatteryManager.EXTRA_STATUS, BatteryManager.BATTERY_STATUS_DISCHARGING)
+            putExtra(BatteryManager.EXTRA_LEVEL, 50)
+            putExtra(BatteryManager.EXTRA_SCALE, 100)
+            putExtra(BatteryManager.EXTRA_VOLTAGE, 4000)
+        })
+        shadowOf(context.getSystemService(BatteryManager::class.java)).apply {
+            setLongProperty(BatteryManager.BATTERY_PROPERTY_CHARGE_COUNTER, 4_000_000L)
+            setLongProperty(BatteryManager.BATTERY_PROPERTY_CURRENT_NOW, currentUa)
+            setLongProperty(BatteryManager.BATTERY_PROPERTY_CURRENT_AVERAGE, currentUa)
+        }
+        battery = BatteryComponent(supplies, vpower).also { it.attach(context); it.start() }
+    }
+
+    private fun assertTelemetry(supplies: File, vpower: File) {
+        val discovered = supplies.listFiles()!!.filter { it.name.contains("BAT") }
+        assertEquals(listOf("BAT1"), discovered.map { it.name })
+        fun read(name: String) = File(discovered.single(), name).readText().trim().toLong()
+        // One 4 Ah battery at 4 V drawing 2 A: 8 W and two hours, regardless of vendor current sign.
+        assertEquals(8_000_000L, read("power_now"))
+        assertEquals(16_000_000L, read("energy_now"))
+        assertEquals(7200L, read("time_to_empty_now"))
+        assertEquals("7200", File(vpower, "secs_until_shutdown_request").readText().trim())
+        assertEquals("50.00", File(vpower, "battery_percent").readText().trim())
+    }
+}