WattBench support

DO NOT PURCHASE THE APP IF YOU DO NOT ALREADY HAVE THE FNB58 DEVICE. WattBench is a companion app for one piece of test equipment, the FNIRSI FNB58 USB power meter. Without the meter it can only show demo data.

What you need

An FNIRSI FNB58 with Bluetooth (FNB58 BT). WattBench talks to the meter over Bluetooth Low Energy. Other FNIRSI meters may share the protocol, but only the FNB58 has been verified.
An iPhone with iOS 17 or later. Widgets and Lock Screen readings work on iOS 17; the Control Center buttons need iOS 18.
Optional: a USB electronic load for the Power Bank Capacity test and the Cable & Charger Check. The Data Cable Check needs no load, just a charger that signals on its data wires.
Optional: a second FNB58 to measure efficiency or a cable's resistance with two meters.

Common questions

"No Meter Found"

Turn Bluetooth on in the meter's own settings menu and keep it within a few metres of the phone. If the meter is connected to another phone or a computer, disconnect it there first. Allow Bluetooth when iOS asks; if you said no, turn it on in iOS Settings → WattBench.

Connected, but the pill says "No data"

WattBench asks the meter to start streaming and retries several times. If the meter stays silent, switch the FNB58 off and on (unplug it for about 10 seconds), check Bluetooth is on in its menu, and connect again. Its Bluetooth module occasionally needs this reset.

Why does my "10,000 mAh" power bank show about 6,000 mAh?

Battery labels quote mAh at the cell's voltage, about 3.7 V; USB runs at 5 V or more, and the bank's converter loses some energy as heat. The power bank test shows both the mAh at the USB port and the cell-equivalent mAh to compare with the label. A healthy bank typically reaches 60–75 % of its rating at the USB port. See Understanding the numbers.

The Data Cable Check can't test my cable

It needs a charger that signals on its data wires: Apple and Samsung chargers and most multi-port USB-A chargers. USB-A to USB-C and USB-A to micro-USB cables work; a USB-C to USB-C cable needs a USB-C charger that signals. Lightning cables can't be tested, because the meter has no Lightning port. See Data Cable Check.

Can I use two meters at once?

Yes, from version 1.3. Turn on Use two meters in Settings, connect your first FNB58, then tap Add a Second Meter… in the Connect sheet. See Two meters.

Does a recording keep going with the phone locked?

Yes. While WattBench is connected to a meter, Bluetooth stays active in the background, so a recording continues with the screen locked and shows on the Lock Screen and Apple Watch. Disconnect when you're done to save battery.

Where are my recordings, and how do I back them up?

On your iPhone, in WattBench's Documents folder (Files app → On My iPhone → WattBench). Nothing is uploaded. Export a session as CSV or PDF to keep a copy elsewhere. Deleting the app deletes its recordings.

Is there a subscription?

No. WattBench is $2.99 on the App Store, with no subscription, account, ads or analytics.

I bought it but don't have an FNB58. Can I get a refund?

Purchases are handled by Apple, so refunds go through Apple too: sign in at reportaproblem.apple.com, find WattBench and choose to request a refund.

Is there a Mac or computer version?

Not of the app. The free, open-source FNB58 desktop web monitor talks to the meter over USB or Bluetooth from a computer.

More answers are in the user guide, including its troubleshooting section.

Contact

Email redthoroughbreds@gmail.com. You'll hear back from Seth, who makes the app. It helps to include:

your iPhone model and iOS version, and the WattBench version;
what you did and what you saw (a screenshot is great);
for connection problems, the diagnostics: gear menu → Diagnostics → Share.

If you use GitHub, you can also open an issue.