Energy Diagnostics

Symptom-based troubleshooting for energy issues. Start with your symptom, follow the decision tree, get the fix.

Related skills: axiom-energy (patterns, checklists), axiom-energy-ref (API reference)

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Symptom 1: App at Top of Battery Settings

Users or you notice your app consuming significant battery.

Diagnosis Decision Tree

App at top of Battery Settings?
│
├─ Step 1: Run Power Profiler (15 min)
│  ├─ CPU Power Impact high?
│  │  ├─ Continuous? → Timer leak or polling loop
│  │  │  └─ Fix: Check timers, add tolerance, convert to push
│  │  └─ Spikes during actions? → Eager loading or repeated parsing
│  │     └─ Fix: Use LazyVStack, cache parsed data
│  │
│  ├─ Network Power Impact high?
│  │  ├─ Many small requests? → Batching issue
│  │  │  └─ Fix: Batch requests, use discretionary URLSession
│  │  └─ Regular intervals? → Polling pattern
│  │     └─ Fix: Convert to push notifications
│  │
│  ├─ GPU Power Impact high?
│  │  ├─ Animations? → Running when not visible
│  │  │  └─ Fix: Stop in viewWillDisappear
│  │  └─ Blur effects? → Over dynamic content
│  │     └─ Fix: Remove or use static backgrounds
│  │
│  └─ Display Power Impact high?
│     └─ Light backgrounds on OLED?
│        └─ Fix: Implement Dark Mode (up to 70% savings)
│
└─ Step 2: Check background section in Battery Settings
   ├─ High background time?
   │  ├─ Location icon visible? → Continuous location
   │  │  └─ Fix: Switch to significant-change monitoring
   │  ├─ Audio active? → Session not deactivated
   │  │  └─ Fix: Deactivate audio session when not playing
   │  └─ BGTasks running long? → Not completing promptly
   │     └─ Fix: Call setTaskCompleted sooner
   │
   └─ Background time appropriate?
      └─ Issue is in foreground usage → Focus on CPU/GPU fixes above

Time-Cost Analysis

Approach	Time	Accuracy
Run Power Profiler, identify subsystem	15-20 min	High
Guess and optimize random areas	4+ hours	Low
Read all code looking for issues	2+ hours	Medium

Recommendation: Always use Power Profiler first. It costs 15 minutes but guarantees you optimize the right subsystem.

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Symptom 2: Device Gets Hot

Device temperature increases noticeably during app use.

Diagnosis Decision Tree

Device gets hot during app use?
│
├─ Hot during specific action?
│  │
│  ├─ During video/camera use?
│  │  ├─ Video encoding? → Expected, but check efficiency
│  │  │  └─ Fix: Use hardware encoding, reduce resolution if possible
│  │  └─ Camera active unnecessarily? → Not releasing session
│  │     └─ Fix: Call stopRunning() when done
│  │
│  ├─ During scroll/animation?
│  │  ├─ GPU-intensive effects? → Blur, shadows, many layers
│  │  │  └─ Fix: Reduce effects, cache rendered content
│  │  └─ High frame rate? → Unnecessary 120fps
│  │     └─ Fix: Use CADisplayLink preferredFrameRateRange
│  │
│  └─ During data processing?
│     ├─ JSON parsing? → Repeated or large payloads
│     │  └─ Fix: Cache parsed results, paginate
│     └─ Image processing? → Synchronous on main thread
│        └─ Fix: Move to background, cache results
│
├─ Hot during normal use (no specific action)?
│  │
│  ├─ Run Power Profiler to identify:
│  │  ├─ CPU high continuously → Timer, polling, tight loop
│  │  ├─ GPU high continuously → Animation leak
│  │  └─ Network high continuously → Polling pattern
│  │
│  └─ Check for infinite loops or runaway recursion
│     └─ Use Time Profiler in Instruments
│
└─ Hot only in background?
   ├─ Location updates continuous? → High accuracy or no stop
   │  └─ Fix: Reduce accuracy, stop when done
   ├─ Audio session active? → Hardware kept powered
   │  └─ Fix: Deactivate when not playing
   └─ BGTask running too long? → System may throttle
      └─ Fix: Complete tasks faster, use requiresExternalPower

Time-Cost Analysis

Approach	Time	Outcome
Power Profiler + Time Profiler	20-30 min	Identifies exact cause
Check code for obvious issues	1-2 hours	May miss non-obvious causes
Wait for user complaints	N/A	Reputation damage

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Symptom 3: Background Battery Drain

App drains battery even when user isn't actively using it.

Diagnosis Decision Tree

High background battery usage?
│
├─ Step 1: Check Info.plist background modes
│  │
│  ├─ "location" enabled?
│  │  ├─ Actually need background location?
│  │  │  ├─ YES → Use significant-change, lowest accuracy
│  │  │  └─ NO → Remove background mode, use when-in-use only
│  │  └─ Check: Is stopUpdatingLocation called?
│  │
│  ├─ "audio" enabled?
│  │  ├─ Audio playing? → Expected
│  │  ├─ Audio NOT playing? → Session still active
│  │  │  └─ Fix: Deactivate session, use autoShutdownEnabled
│  │  └─ Playing silent audio? → Anti-pattern for keeping app alive
│  │     └─ Fix: Use proper background API (BGTask)
│  │
│  ├─ "fetch" enabled?
│  │  └─ Check: Is earliestBeginDate reasonable? (not too frequent)
│  │
│  └─ "remote-notification" enabled?
│     └─ Expected for push updates, check didReceiveRemoteNotification efficiency
│
├─ Step 2: Check BGTaskScheduler usage
│  │
│  ├─ BGAppRefreshTask scheduled too frequently?
│  │  └─ Fix: Increase earliestBeginDate interval
│  │
│  ├─ BGProcessingTask not using requiresExternalPower?
│  │  └─ Fix: Add requiresExternalPower = true for non-urgent work
│  │
│  └─ Tasks not completing? (setTaskCompleted not called)
│     └─ Fix: Always call setTaskCompleted, implement expirationHandler
│
└─ Step 3: Check beginBackgroundTask usage
   │
   ├─ endBackgroundTask called promptly?
   │  └─ Fix: Call immediately after work completes, not at expiration
   │
   └─ Multiple overlapping background tasks?
      └─ Fix: Track task IDs, ensure each is ended

Common Background Drain Patterns

Pattern	Power Profiler Signature	Fix
Continuous location	CPU lane + location icon	significant-change
Audio session leak	CPU lane steady	setActive(false)
Timer not invalidated	CPU spikes at intervals	invalidate in background
Polling from background	Network lane at intervals	Push notifications
BGTask too long	CPU sustained	Faster completion

Time-Cost Analysis

Approach	Time	Outcome
Check Info.plist + BGTask code	30 min	Finds common issues
On-device Power Profiler trace	1-2 hours (real usage)	Captures real behavior
User-collected trace	Variable	Best for unreproducible issues

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Symptom 4: High Energy Only on Cellular

Battery drains faster on cellular than WiFi.

Diagnosis Decision Tree

High battery drain on cellular only?
│
├─ Expected: Cellular radio uses more power than WiFi
│  └─ But: Excessive drain indicates optimization opportunity
│
├─ Check URLSession configuration
│  │
│  ├─ allowsExpensiveNetworkAccess = true (default)?
│  │  └─ Fix: Set to false for non-urgent requests
│  │
│  ├─ isDiscretionary = false (default)?
│  │  └─ Fix: Set to true for background downloads
│  │
│  └─ waitsForConnectivity = false (default)?
│     └─ Fix: Set to true to avoid failed connection retries
│
├─ Check request patterns
│  │
│  ├─ Many small requests? → High connection overhead
│  │  └─ Fix: Batch into fewer larger requests
│  │
│  ├─ Polling? → Radio stays active
│  │  └─ Fix: Push notifications
│  │
│  └─ Large downloads in foreground? → Could wait for WiFi
│     └─ Fix: Use background URLSession with discretionary
│
└─ Check Low Data Mode handling
   ├─ Respecting allowsConstrainedNetworkAccess?
   │  └─ Fix: Set to false for non-essential requests
   │
   └─ Checking ProcessInfo.processInfo.isLowDataModeEnabled?
      └─ Fix: Reduce payload sizes, defer non-essential transfers

Time-Cost Analysis

Approach	Time	Outcome
Review URLSession configs	15 min	Quick wins
Add discretionary flags	30 min	Significant savings
Convert poll to push	2-4 hours	Largest impact

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Symptom 5: Energy Spike During Specific Action

Noticeable battery drain or heat when performing particular operation.

Diagnosis Decision Tree

Energy spike during specific action?
│
├─ Step 1: Record Power Profiler during action
│  └─ Note which subsystem spikes (CPU/GPU/Network/Display)
│
├─ CPU spike?
│  │
│  ├─ Is it parsing data?
│  │  ├─ Same data parsed repeatedly?
│  │  │  └─ Fix: Cache parsed results (lazy var)
│  │  └─ Large JSON/XML payload?
│  │     └─ Fix: Paginate, stream parse, or use binary format
│  │
│  ├─ Is it creating views?
│  │  ├─ Many views at once?
│  │  │  └─ Fix: Use LazyVStack/LazyHStack
│  │  └─ Complex view hierarchies?
│  │     └─ Fix: Simplify, use drawingGroup()
│  │
│  └─ Is it image processing?
│     ├─ On main thread?
│     │  └─ Fix: Move to background queue
│     └─ No caching?
│        └─ Fix: Cache processed images
│
├─ GPU spike?
│  │
│  ├─ Starting animation?
│  │  └─ Fix: Ensure frame rate appropriate
│  │
│  ├─ Showing blur effect?
│  │  └─ Fix: Use solid color or pre-rendered blur
│  │
│  └─ Complex render? (shadows, masks, many layers)
│     └─ Fix: Simplify, use shouldRasterize, cache
│
├─ Network spike?
│  │
│  ├─ Large download started?
│  │  └─ Fix: Use background URLSession, show progress
│  │
│  ├─ Many parallel requests?
│  │  └─ Fix: Limit concurrency, batch
│  │
│  └─ Retrying failed requests?
│     └─ Fix: Exponential backoff, waitsForConnectivity
│
└─ Display spike?
   └─ Unusual unless changing brightness programmatically
      └─ Fix: Don't modify brightness, let system control

Time-Cost Analysis

Approach	Time	Outcome
Power Profiler during action	5-10 min	Identifies subsystem
Time Profiler for CPU details	10-15 min	Identifies function
Code review without profiling	1+ hours	May miss actual cause

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Quick Diagnostic Checklist

Use this when you need fast answers:

30-Second Check

• Device plugged in? (Power metrics show 0)
• Debug build? (Less optimized than release)
• Low Power Mode on? (May affect measurements)

5-Minute Check (Power Profiler)

• Which subsystem is dominant? (CPU/GPU/Network/Display)
• Sustained or spiky?
• Foreground or background?

15-Minute Investigation

• If CPU: Run Time Profiler to identify function
• If Network: Check request frequency and size
• If GPU: Check animation frame rates
• If Background: Check Info.plist modes

Common Quick Fixes

Finding	Quick Fix	Time
Timer without tolerance	Add .tolerance = 0.1	1 min
VStack with large ForEach	Change to LazyVStack	1 min
allowsExpensiveNetworkAccess = true	Set to false	1 min
Missing stopUpdatingLocation	Add stop call	2 min
No Dark Mode	Add asset variants	30 min
Audio session always active	Add setActive(false)	5 min

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When to Escalate

Use axiom-energy skill when

• Need full audit checklist
• Want comprehensive patterns with code
• Planning proactive optimization

Use axiom-energy-ref skill when

• Need specific API details
• Want complete code examples
• Implementing from scratch

Use energy-auditor agent when

• Want automated codebase scan
• Looking for anti-patterns at scale
• Pre-release energy audit

Run: /axiom:audit energy

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Last Updated: 2025-12-26 Platforms: iOS 26+, iPadOS 26+