Juicer

A controlled macOS battery-drain utility for testing low-power behavior.

Demo

Juicer intentionally increases power draw until your MacBook reaches a target battery percentage, then it stops and restores brightness. It is useful for testing low-battery UX, battery warnings, power-mode behavior, and anything that only appears when charge drops quickly.

Highlights

Area	What Juicer Does
Controlled drain	Stops automatically at the target battery percentage.
Power modes	Strong, Turbo, and Max let you choose how aggressive the workload should be.
Safer workload	Uses bounded CPU, Core Image, memory, and temporary disk work instead of unbounded crash-prone allocations.
Battery-aware UI	Shows current charge, start eligibility, runtime, workers, and operations per second.
Cleanup	Restores sleep assertions and screen brightness when stopped.

Power Modes

Mode	Workload	Best For
Strong	CPU workers plus display brightness boost	Routine low-battery testing
Turbo	More CPU workers plus Core Image rendering	Faster, still controlled drain
Max	CPU, graphics, memory pressure, and bounded temp disk churn	Aggressive drain tests

Quick Start

git clone <your-repo-url>
cd Juicer
./build.sh
open build/Juicer.app

You can also type-check the Swift sources directly:

xcrun swiftc -typecheck \
  Sources/Juicer/JuicerApp.swift \
  Sources/Juicer/ContentView.swift \
  Sources/Juicer/BatteryManager.swift \
  -framework AppKit \
  -framework SwiftUI \
  -framework IOKit \
  -framework Foundation \
  -framework CoreGraphics \
  -framework CoreImage \
  -framework Combine

Usage

1. Launch Juicer.
2. Set a target percentage below the current battery level.
3. Pick a power mode.
4. Click Start Juicing.
5. Stop manually or let Juicer stop automatically at the target.

Important: Max mode is intentionally heavy. Save active work before running it.

Project Layout

.
├── Assets/README/        # README images and animation
├── Sources/Juicer/       # SwiftUI app and battery drain engine
├── Info.plist            # App bundle metadata
├── Package.swift         # SwiftPM manifest
├── build.sh              # Local app-bundle build script
└── README.md

How It Works

Juicer combines several power-drain techniques while keeping each one bounded:

• prevents idle/display sleep while active
• boosts display brightness and restores it on stop
• runs CPU workers sized from activeProcessorCount
• renders Core Image frames in Turbo and Max modes
• uses temporary disk churn only in Max mode
• polls the internal battery and stops at the target percentage

Safety and cleanup behavior

• Temp disk files are written under macOS temporary storage and removed by the worker that created them.
• Brightness is restored only if Juicer successfully captured the original value.
• Sleep assertions are released on stop and deinitialization.
• Juicer does not make network requests.

Development

./build.sh
open build/Juicer.app

The build output is ignored by Git. Source changes live under Sources/Juicer/.

Upload Notes

This repo is ready to publish once you choose a license. The generated app bundle and Swift build products are ignored by .gitignore.