Reading a battery health report
How to read a battery health figure, what the cycle count adds to it, and which thresholds hold.
The reading sequence
4 steps, starting at handover and completeness and running to confirm the figure with a discharge check. Evidence on this point is read at E1, and 2 of the 4 steps carries a condition that ends the assessment outright.
Get the report photographed with the unit's own identifier
Make sure the health figure belongs to the unit in the conversation rather than to a screenshot from somewhere else.
Evidence: E1 — one photo of the battery panel on screen with a device identifier visible in the same frame, plus one of the system information panel
- The battery panel and a device identifier appear in a single frame.
- The panel is the operating system's own screen rather than a third-party overlay.
- The battery panel is shown while the identifier sits in a separate photo.
- The panel is legible but too small to read the design capacity field.
- The screenshot shows no identifier and no system interface around it.
- The figure comes from a utility that does not state how it derives its number.
Read the three fields as one set
Read design capacity, current full charge capacity and cycle count together, because a health percentage on its own hides which of the three moved.
Evidence: E1 — the step 1 photo, read at all three fields with the figures written down
- All three fields are legible, and the health percentage can be recomputed from the first two.
- The design capacity matches the capacity this model is specified with.
- The health percentage is shown without the design and current capacity fields.
- The cycle count is given as a rounded figure or a range rather than a number.
- The design capacity field reads zero, or the panel reports no battery data at all.
- The design capacity is a different value from the one this model is specified with.
Place the two figures in a band
Sort the report into one of three bands using the cycle count and the recomputed health together, rather than the percentage alone.
Evidence: E1 — the three fields written down in step 2, read against the bands below
- Cycle count under 300 and recomputed health at 90 per cent or above.
- Both figures fall inside the same band, so neither contradicts the other.
- Cycle count between 300 and 600, or recomputed health between 85 and 90 per cent.
- One figure sits inside a band while the other sits just outside it.
- Cycle count above 800, or recomputed health below 80 per cent.
- The unit reports very few cycles for its apparent age while health sits in the bottom band.
Confirm the figure with a discharge check
Replace the computed figure with a measured one by watching the charge percentage fall under a stated load.
Evidence: E1 — a video of thirty minutes of screen-on use at a stated brightness, with the percentage before and after both visible and a clock in frame
- The percentage falls by no more than the capacity figure predicts over that period.
- The start percentage, the end percentage and a clock all appear in the same video.
- The video covers ten minutes rather than thirty, which is too short to separate two bands.
- The brightness is not stated, so the load cannot be repeated by anyone else.
- The percentage falls about twice as fast as the capacity figure predicts.
- The unit shuts down while a percentage is still showing on screen.
Why the thresholds sit where they do
A battery percentage is a computed figure, not a measurement: it is derived by dividing one reported capacity by another, and both of those numbers come from the same controller. Reading the three fields together is therefore what makes the figure checkable, because a percentage can be recomputed and a design capacity can be compared against the capacity the model is specified with. The 300 and 800 cycle bands and the 90 and 80 per cent health bands are set from the shape of the curve rather than from a single test: capacity loss is slow for the first few hundred cycles and then steepens, so a unit in the middle band is a normal used unit while a unit in the bottom band has moved past the flat part of the curve. The discharge check exists because the controller's own numbers can drift away from behaviour, and half an hour under a stated load is the shortest test that separates the upper band from the lower one.
Common misreads
2 pairs recorded for this point. Each runs in both directions: 1 finding that looks worse than it is, and 1 that looks better.
- looks like Return actually Pass
A health figure of 78 per cent in a third-party utility on a unit whose own panel reports 91 per cent. The utility applies its own formula to the same two fields, and the bands are written for the panel.
- looks like Pass actually Return
A clean screenshot of a battery panel showing 96 per cent with no identifier in frame. An encouraging figure with nothing attached to it cannot be told apart from one taken from a different unit.
Check this point against what you were sent
Insufficient evidence
Nothing decided on battery health report reading yet: 0 of 4 steps have been read.
0 of 4 steps judged
| Step | Reading | Evidence | Stop met |
|---|---|---|---|
| 1. Get the report photographed with the unit's own identifierneeds E1 | — | ||
| 2. Read the three fields as one setneeds E1 | The design capacity field reads zero, or does not match the capacity the model is specified with. The percentage printed beside it is then computed from a figure that cannot be checked against anything. | ||
| 3. Place the two figures in a bandneeds E1 | — | ||
| 4. Confirm the figure with a discharge checkneeds E1 | The unit shuts down with charge still showing, or falls at about twice the predicted rate. The report and the behaviour disagree, and the behaviour is the measurement rather than the estimate. |
Sources and checks
- Public community thread — Threads where a health figure was quoted without the fields behind itn=45
- Editor analysis — Cycle and health bands set from the shape of published capacity-loss curvesno sample
Last checked · next review due · status current.
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