Diagnose
Unplugged, and half the machine. Measure the gap instead of guessing it.
On battery most laptops drop to a lower sustained power limit. The test flags a run on battery and compares it against one plugged in, so the gap is a number.
What the report tells you
Three figures, each with its reading.
Battery flag
on battery
The report marks a run made on battery and never compares it against a plugged-in run as an equal.
The gap
%
Run plugged in, run on battery. The before/after comparison overlays the two curves and states the difference per figure.
Charge used
%
How much of the battery the run consumed, which is the sustained wattage seen from the other side.
The diagnosis
The shape of the curve, read for your case.
01A lower step on battery
The battery power limit. This is the design, and the vendor's power tool is the only place it changes.
02A slide on both
Cooling, not the battery. Fixing the cooling helps both runs.
03Held on both
The laptop does not limit itself on battery, or its cooler is the limit either way. Unusual, and worth knowing.
Every class comes with a stated confidence and the measurement’s own noise floor. How the shape is read
Where a browser stops
What it cannot tell you.
- No battery health or capacity: the report reads the charge used during the run, not the cell's wear.
- The battery API is not available in every browser; where it is not, the flag is absent rather than guessed.
- No power draw in watts: the charge used across the run is the closest a browser can get.
Which run
Standard, 3 minutes.
Two standard runs, one plugged in and one not, are enough to measure the gap. Run the same kind both times so the comparison is fair.
Both kinds are free. The choice is on the set-up screen.
Questions
Asked in these words.
- Why is my laptop so slow on battery?
- Most laptops switch to a lower sustained power limit on battery to protect the cell and extend runtime. The performance loss is the size of that limit. Run the test once plugged in and once on battery; the report compares the two and states the difference.
- Can I make my laptop as fast on battery as plugged in?
- Usually not fully. The vendor's power tool can raise the battery limit at the cost of runtime and heat. The comparison shows how much a setting change recovered.
- Does the test drain the battery?
- A standard run uses a few percent on most laptops; the report states how much. A deep run uses proportionally more.