Where the rules come from
Sources
Every rule Laptop Services uses comes from one of these public pages, in our own words. Anything else is marked as this site's rule of thumb or as an assumption.
- Microsoft Learn: Powercfg command-line options (/batteryreport)
- Apple Support: Determine battery cycle count for Mac laptops
- FAA PackSafe: Lithium batteries
- Linux kernel documentation: Power supply class (ENERGY_FULL, ENERGY_FULL_DESIGN)
- USB-IF: USB Charger (USB Power Delivery): up to 100 W, and up to 240 W with USB PD 3.1 and a 240 W cable
What comes from where
- How to make a Windows battery report (
powercfg /batteryreport): Microsoft Learn. - The 80% mark: Apple says its Mac laptop batteries are designed to keep up to 80% of their original capacity at their maximum cycle count (1,000 cycles for recent models; check your model on Apple's page). Laptop Services uses the same mark for every laptop as a general guide.
- The 60% "heavily worn" line: this site's rule of thumb, not a maker's figure.
- Flight rules for lithium ion batteries and power banks (100 Wh, 101 to 160 Wh with airline approval and up to two spares, carry-on only): FAA PackSafe.
- USB-C charging: USB Power Delivery lets a laptop and charger agree on power, up to 100 W, or up to 240 W with USB PD 3.1 and a 240 W cable (USB-IF). How a laptop behaves on a smaller charger is up to the laptop; the charger thresholds (100% and 60% of your own charger's watts) are this site's rule of thumb.
- Power bank charges assume about 80% of the bank's energy reaches the laptop: an assumption; real losses vary.
- Linux battery numbers: the kernel's power supply class (ENERGY_FULL, ENERGY_FULL_DESIGN), as shown by
upower.
Pages move. If a link no longer works, search the title on the publisher's site.