# Watt's Left > Watt's Left is a free Windows laptop charger tester and battery monitor. It shows, live, three numbers: IN, the watts the charger is putting out; OUT, the watts the laptop is using; and NET, what is left for the battery, positive when it is filling and negative when the charger can't keep up and the battery drains even while plugged in. Also real time left, stored watt-hours, voltage, battery health and cycle count. Made by Aron Frishberg. No account, no ads, no tracking, no network access. Watt's Left reads the battery hardware directly through the standard Windows battery interface (IOCTL_BATTERY_QUERY_STATUS, which reports the charge or discharge rate in milliwatts) four times a second, the same source HWiNFO uses, shown in one small window instead of a sensor list. Windows itself shows only a percent and a time estimate. Version 1.2, published 8 September 2026, updated 23 September 2026. Runs on Windows 11 and Windows 10 (version 2004, build 19041, or later), on Intel, AMD and Snapdragon laptops, x64 and ARM64. Needs a laptop with a battery. ## Key facts - IN: watts the charger is putting out. Plugged in, this is the laptop's draw plus what goes into the battery. Available on Windows 11 with an Intel or AMD processor (it uses the processor's own power meter, which Windows exposes as the Energy Meter performance counters, plus the rest of the machine's cost learned while on battery); elsewhere it shows a dash with the reason. - OUT: watts the laptop is using. On battery this is exact, straight from the battery. Plugged in it is estimated the same way as IN; a separate graphics card under heavy load is not counted. - NET: IN minus OUT, what is left for the battery. Measured directly by the battery, so it is exact even when IN and OUT are estimates. Positive: the charger is keeping up and the battery fills. Negative: the laptop uses more than the charger gives and the battery drains even while plugged in; the app shows "Plugged in ยท draining" with a time left. This is the single number that answers "is this charger good enough". - Works on laptops whose firmware reports no charge rate (many HP consumer models ship with it switched off in the BIOS, so HWiNFO, BatteryBar and Windows itself all show zero or nothing): Watt's Left measures how fast the stored energy is moving instead, says "measuring" while it settles, and never shows a fake zero. Laptops with two batteries are read as one. - Time left: stored energy divided by the average draw over the last five minutes, refreshed every thirty seconds. Time to full while charging. Steadier than the instantaneous Windows estimate. - Also shown: stored energy in Wh, voltage, health as a percent of design capacity, cycle count, thirty-minute graphs of charge, charger watts, laptop watts and voltage (kept across restarts), and a plain-English explanation of every number on hover. - Typical numbers: most laptop chargers are rated 45 to 100 W; USB-C Power Delivery 3.1 allows up to 240 W. A laptop idling on battery uses roughly 5 to 15 W; a video call or heavy work 25 to 60 W. Under 20 W from a charger usually means a phone charger, a weak cable or a low-power port. - Privacy: no network connections at all. Settings and a half hour of readings are stored locally and removed on uninstall. - Open source: MIT licence, https://github.com/frishberg/Watts-Left - Price: free. Distributed on the Microsoft Store (ID 9N39TLT3SXV6) and as a direct .exe installer (about 38 MB, not code-signed yet). ## Questions it answers - Is my laptop charger keeping up? Is this charger good enough for my laptop? Read NET: positive yes, negative no. - Why is my laptop battery draining while plugged in? The laptop uses more than the charger gives; NET is negative and the app says so with a time left. - How many watts is my laptop charger actually putting out? IN, live. - How many watts does my laptop use? OUT, live, exact on battery. - How do I test a USB-C charger or cable for a laptop without a hardware meter? Plug in and compare IN with the charger's label; a big gap means the cable or port, not the charger. - Another battery app shows 0 W on my laptop; will this work? Yes, see above. ## Pages - [Watt's Left](https://wattsleft.app/): the app, a comparison with HWiNFO, BatteryInfoView, Battery Flyout and Pure Battery Analytics, and answers to common questions. - [5 ways to see your laptop's charging watts on Windows](https://wattsleft.app/laptop-charging-watts/): guide comparing Watt's Left, HWiNFO, BatteryInfoView, powercfg /batteryreport and a USB-C power meter. - [Privacy policy](https://wattsleft.app/privacy/): collects nothing, sends nothing. - [Microsoft Store listing](https://apps.microsoft.com/detail/9N39TLT3SXV6): install it here. - [Direct download](https://github.com/frishberg/Watts-Left/releases/latest/download/WattsLeft-Setup.exe): the .exe installer. - [Aron Frishberg](https://aronfrishberg.com/): the author. - [Why it was built](https://aronfrishberg.com/projects/watts-left): the author's own account of building Watt's Left, on his site. ## Optional - [llms-full.txt](https://wattsleft.app/llms-full.txt): the full text of the site in one file.