I had a new charger and wanted to test one thing: is it actually sustaining my computer, or is my laptop slowly dying? The only way to find out was a random app called HWiNFO, a sensor tool usually used by very technical overclockers, and even then I had to scroll past dozens of CPU and GPU readings to find a single value about the battery. So I built the app I needed. One window, nothing else. Open source, so no one else has to have the same issue.

Get it on the Microsoft Store wattsleft.app Source on GitHub

Three numbers

The battery in your laptop knows one thing: how many watts are flowing into it or out of it right now. Windows reads that four times a second and shows you a percent. Watt's Left shows you the number, and two more around it. IN is what the charger gives. OUT is what the laptop uses. NET is what's left for the battery, which is just IN minus OUT.

The top of the Watt's Left window: IN 48.5 W charger, OUT 16.9 W est. laptop, NET 31.6 W
IN minus OUT is NET. If NET is positive, the charger is winning.

NET is the whole point. Positive means the battery is filling. Negative means the laptop is using more than the charger can give, and the battery is slowly draining even though it's plugged in. The app says "Plugged in · draining" and tells you how long you've got. That was my question with the new charger, answered in one glance.

Getting IN and OUT was the interesting part, because Windows only tells you what reaches the battery. Plugged in, the laptop runs off the wall first and the battery gets the rest, so the battery can't tell you what the charger is putting out. What Windows 11 does expose is the processor's own power meter, which covers most of what a laptop burns but not the screen, drive, or Wi-Fi. So the app learns the rest while you're on battery, where the true draw is known, remembers it, and from then on can show what the laptop uses and what the charger gives while plugged in. It's marked as an estimate. NET is measured directly by the battery and is exact.

The Watt's Left window with a hover card open beside OUT, reading: Energy the laptop is using. Lately about 24 W, estimated while plugged in.
Hover anything and it explains itself in two plain sentences.

The rest is taste. The numbers refresh once a second so the window reads like a gauge, not a ticker. Time left comes from a five-minute average of what you're actually doing. There are thirty-minute graphs of charge, charger watts, laptop watts, and voltage, one toggle away. It makes no network connections at all, it lives in your tray, and it's free.

The little dancing guy

Somewhere in the middle of building this I added a little stick figure who dances on the charged part of your battery bar, and I got really into it. He climbs down a ladder when you turn him off. He cries when you unplug. You can pick him up by his hands and swing him around the window. None of this has anything to do with watts, and I spent an embarrassing amount of time on it.

Then I decided the funniest thing I could do was deny he exists, everywhere, forever. The website says "Definitely no little dancing guy." The FAQ says "Absolutely not." The Store listing has a screenshot with him plainly visible under the words "These wild rumors are speculative and baseless. Next question." I'm not going to break the bit here either. There is no little dancing guy.

The Watt's Left window at 91% charge, with nothing unusual on the charge bar whatsoever
Nothing to see here.

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