WattBench

WattBench turns your iPhone into a wireless display, data logger and test bench for the FNIRSI FNB58 USB power meter.

Connect over Bluetooth and watch voltage, current and power live. See what your charger is doing on the USB data lines. Record a whole charge cycle with the phone locked. Then run guided tests that answer real questions: how much a power bank actually holds, how fast a phone really charges, and whether a cable is wasting power.

LIVE
• Big, glanceable voltage, current and power with peak hold
• USB data lines: D+ and D− voltages and the meter's temperature
• Charger detection: Quick Charge, USB PD, Apple, Samsung and BC 1.2 patterns named automatically
• Chart of V, A or W, or All: voltage, current and power as three stacked charts on one time axis, each with its own scale
• Full-screen chart up to the last 60 minutes, in portrait or landscape, with pinch to zoom and one cursor across all three charts
• Trip counter for energy (Wh) and capacity (mAh) without starting a recording

TESTS
• Power Bank Capacity: compares what a bank really delivers with the mAh on its label
• Device Charge: shows the fast, tapering and trickle phases of a charge, with a battery estimate
• Cable & Charger Check: guides you through load steps with a USB electronic load and grades the resistance of the cable and charger
• Data Cable Check: finds out in about a minute whether a USB cable can carry data or only charge, using a charger that signals on its data wires

TWO METERS
• Use two FNB58s at once, one before and one after a charger, cable or adapter (turn on Use two meters in Settings)
• Efficiency: power in, power out, efficiency and the energy lost
• Cable: the cable's resistance from the voltage drop between the two meters
• Compare: two ports or devices side by side
• Match Meters takes out the small offset between your two meters
• Record both meters into one session, with both in the CSV and PDF report

RECORDINGS AND REPORTS
• Recordings keep running with the screen locked and survive a crash or a Bluetooth drop; dropouts are shown honestly as gaps
• Lock Screen, Dynamic Island and Apple Watch Smart Stack show live readings while you record
• Home Screen, Lock Screen and StandBy widgets show your latest recording or the one in progress; Control Center buttons start a recording or open live readings (iOS 18)
• Automatic markers when the charger changes mode or voltage
• Session reports with zoomable charts (V, A, W or all three stacked), range statistics, a power histogram, a voltage-versus-current plot, cumulative energy, temperature and D+/D− over time
• Compare up to four sessions on one chart
• Export PDF reports and CSV files

ALERTS
• Over- and under-voltage, over-current, over-power, current below, voltage drop, disconnect, over-temperature and "fast charge lost", with presets
• Banners in the app, notifications in the background, with Stop & save during a recording

PRIVATE BY DESIGN
No account, no ads, no analytics, no network access. Your recordings stay on your iPhone.

REQUIREMENTS
The FNIRSI FNB58 USB power meter with Bluetooth. Turn Bluetooth on in the meter's settings menu, then tap Connect. A USB electronic load is recommended for the power bank test and the Cable & Charger Check. Two-meter mode needs a second FNB58. No meter yet? Tap Try Demo Data to explore every screen.

User guide and test recipes: https://redthoroughbred.github.io/wattbench/guide.html

WattBench is an independent project and is not affiliated with or endorsed by FNIRSI.