LockDown Browser Battery Drain on Mac (Per-Hour Cost + Mitigations)
LockDown Browser with Respondus Monitor enabled drains 5-12% of battery per hour on Apple Silicon Macs at 50% screen brightness - meaningfully more than Safari (~5%) but less than Chrome (~16%). Below: per-chip rates, what increases drain, and how to extend battery for long exams.
Per-chip drain rates (LDBypass benchmark, 90-min exam, 50% brightness)
| Mac | Drain per hour (LDB attributed) | 3-hour exam total |
|---|---|---|
| MacBook Air M2 16 GB | ~10.4% | ~32% |
| MacBook Pro M3 Pro 18 GB | ~7.8% | ~24% |
| MacBook Pro M4 Pro 24 GB | ~6.1% | ~19% |
| MacBook Pro M4 Max 36 GB | ~5.4% | ~17% |
Compare to Safari + LMS exam in normal browser tab: ~5.1% per hour on the same M2 Air. LDB + Monitor is ~2× the cost of plain Safari.
What increases battery drain
| Factor | Additional drain per hour |
|---|---|
| Screen brightness 80% vs 50% | +3-4% |
| External display attached | +5-8% |
| Low Power Mode disabled (vs enabled) | +2-3% |
| Bluetooth on with active connection (AirPods) | +1-2% |
| Real-time AV scanning Monitor frames | +3-5% |
| Cloud sync running | +1-2% |
| Spotlight indexing | +2-3% |
| Wi-Fi unstable / weak signal | +1-2% (constant retransmit) |
| Intel-build LDB via Rosetta | +30-50% relative |
Extension strategies for long exams (>2 hours unplugged)
- Charge to 100% the night before, not the morning of. Trickle-charging from 80-100% takes longer than fast-charging from 0-80%.
- Enable Low Power Mode in System Settings → Battery before launching LDB. Reduces brightness ramping, defers Spotlight, halves background CPU budget.
- Set screen brightness to ≤50%. Each step above 50% costs ~3% per hour.
- Disable Bluetooth if you're using built-in mic. Bluetooth idle alone is ~2-3% per hour.
- Quit every other application before launching LDB. Slack/Teams in tray = wasted 1-2%/hr each.
- Pause AV products. Critical - AV easily costs 5%/hr extra.
- Use cellular hotspot only if Wi-Fi is unreliable; otherwise stick to Wi-Fi (cellular costs more).
- For >3 hour exams: plug in. The marginal cost of being plugged in is zero; the cost of dying mid-exam is enormous.
If your battery is dying faster than expected
- Check battery health: System Settings → Battery → Battery Health. Below 80% = aging battery; replacement may be needed.
- Verify charge cable + power adapter. Some third-party USB-C adapters provide insufficient wattage.
- Check for stuck high-CPU processes other than LDB (see high-CPU page).
Battery dying mid-exam - emergency procedure
If your Mac warns about low battery during the exam:
- Plug in if possible. macOS continues the exam through the charge connection.
- If you can't plug in, save your current question by clicking Next/Previous (LMS auto-save).
- If you reach 5% battery, the Mac will sleep. LDB doesn't recover gracefully from sleep mid-exam.
- Force-quit LDB (⌘+⌥+Esc) before sleep - at least the answers up to that point are preserved.
- Email instructor immediately with the time of failure.
Frequently asked questions
Why does LDB drain more than Safari?
Monitor records webcam + microphone + screen continuously, encoding video in real time. That's a meaningful CPU + GPU + storage I/O cost that Safari (just rendering a webpage) doesn't pay.
Does plugging in during the exam look suspicious?
No - Monitor records what's on camera. Plugging in your laptop is normal behavior, not flagged.
Will Low Power Mode affect my exam UI smoothness?
Marginally. Low Power Mode caps display refresh on Pro models (120Hz → 60Hz) and reduces background CPU. The exam UI is text + multiple-choice; you won't notice the difference.