Battery profiling

Battery Profiling

Instructions

Battery drain is always attributable — CPU, radio wakeups, GPS, screen brightness, or unreleased wakelocks. This skill shows how to capture a reliable energy trace and how to read it.

1. What to Measure

• mAh per hour in a representative workload (idle, active feed, video).
• CPU time (user + kernel).
• Radio time (Wi-Fi on, cellular on, data transfer).
• Wakelocks / assertions count and duration.
• GPS / sensor active time.
• Screen on-time at which brightness.

Budgets (rule of thumb):

State	Foreground (%/h)	Background (%/h)
Idle	< 3	< 0.5
Browsing	< 8	—
Video	< 15	—

2. Android — Battery Historian

1. adb shell dumpsys batterystats --reset

2. Unplug the device. Use the app for 10–20 minutes.

3. adb bugreport bugreport.zip

4. Open Battery Historian or run locally via Docker:

   docker run -p 9999:9999 bhaavan/battery-historian
   

5. Upload bugreport.zip. Inspect:

   • Wakelocks — per-app held wakelocks. Any partial wakelock > 30 s is suspect.
   • Kernel wakeups — modem, Wi-Fi, alarm. Reduce with JobScheduler / WorkManager constraints.
   • Process CPU — top processes while screen-off.
   • Doze transitions — confirm the app respects Doze (no network during idle maintenance windows).

3. Android — On-Device Energy Profiler

Android Studio Profiler → Energy row on API 26+. Shows a unit-less high/medium/low indicator with a breakdown:

• CPU
• Network (radio-on cost + transfer cost)
• Location (GPS on)

Click a bar to see wakelock, alarm, and job events with stack traces — correlates code to energy cost.

4. iOS — Instruments Energy Log + Xcode Gauges

Xcode debugger gauge panel shows live Energy Impact. For reproducible measurements:

1. Product → Profile → Energy Log template (requires a physical device, ideally unplugged — use wireless debugging).

2. Record for 2–5 minutes under the scenario.

3. Track views:

   • Energy Usage — high/low bars per second.
   • CPU Activity — user vs kernel.
   • Networking — bytes in/out and connection lifetime.
   • Location — GPS/Wi-Fi scan activity.
   • Display Brightness, Bluetooth, etc.

4. Generate a diagnostic .logarchive:

   xcrun simctl spawn booted log collect
   

MetricKit in production:

class Delegate: NSObject, MXMetricManagerSubscriber {
    func didReceive(_ payloads: [MXMetricPayload]) {
        for p in payloads {
            let cpu = p.cpuMetrics.cumulativeCPUTime
            let cells = p.cellularConditionMetrics
            // ship to telemetry
        }
    }
}

5. Common Drain Sources

Symptom	Likely cause	Fix
High radio time even when idle	Chatty polling, small requests every 5–30 s	Batch, lengthen interval, use silent push.
Sustained wakelock	PARTIAL_WAKE_LOCK held across network retry loops	Use WorkManager with NetworkType.CONNECTED; drop explicit lock.
High CPU while screen off	Infinite timers, MQTT reconnect storm	Exponential backoff, FCM push instead of polling.
GPS active for minutes	"Always" location permission, foreground tracking bugs	Use significant-change / geofence APIs; stop when not needed.
Bluetooth always scanning	BLE scan without filters	Use ScanFilter + SCAN_MODE_LOW_POWER.
iOS "high energy" from WebView	Animated GIFs, complex CSS, autoplay video	Pause WebView on disappear; freeze animations.

6. Guardrails in Code

Kotlin — prefer coroutines with cancellation and network constraints:

val req = OneTimeWorkRequestBuilder<SyncWorker>()
    .setConstraints(
        Constraints.Builder()
            .setRequiredNetworkType(NetworkType.UNMETERED)
            .setRequiresBatteryNotLow(true)
            .setRequiresCharging(false)
            .build()
    ).build()
WorkManager.getInstance(ctx).enqueue(req)

Swift — use BGProcessingTaskRequest with requiresExternalPower/requiresNetworkConnectivity:

let req = BGProcessingTaskRequest(identifier: "com.app.sync")
req.requiresNetworkConnectivity = true
req.requiresExternalPower = false
try BGTaskScheduler.shared.submit(req)

7. Compare Before/After

Always compare two runs with the same workload, same starting battery level, same network conditions. Tools:

• Android Automator + monkey for reproducible workloads.
• XCUITest + XCTApplicationLaunchMetric/custom metrics for iOS.

Checklist

• Energy baseline captured with an identical, scripted workload.
• Battery Historian shows no unexpected wakelock > 30 s.
• Energy Log / MetricKit MXCPUMetric shows CPU time within budget.
• No radio-on polling on the background path; push or batched sync only.
• GPS / BLE scanning uses filtered, low-power APIs.
• Background work uses WorkManager / BGTaskScheduler with constraints.
• Regression dashboard fed by MetricKit payloads in production.