PRESET-RATIONALE.md

Preset Threshold Rationale

This document explains the default threshold values used by threshpad's preset modes and the sources they are based on.

The Trade-off

Lithium-ion batteries degrade faster when kept at high state-of-charge for extended periods. Charge thresholds limit how high the battery charges, trading some runtime capacity for longer calendar lifespan.

• Lower thresholds → longer battery lifespan, less runtime when unplugged
• Higher thresholds → shorter battery lifespan, more runtime when unplugged

Preset Values

Mode	Start	Stop	Rationale
Desk Mode	40%	50%	Always plugged in; maximize lifespan over runtime
Balanced	75%	80%	Mixed use; good compromise between lifespan and runtime
Travel Prep	0%	100%	Charge fully before a trip; revert to Balanced after

These values are consistent across both BAT0 and BAT1. There is no documented basis for treating an internal vs. swappable ThinkPad battery differently for threshold purposes — both cells age the same way.

Sources

• TLP Project — Battery Care FAQ https://linrunner.de/tlp/faq/battery.html Canonical reference for ThinkPad battery threshold configuration. Recommends START=40 / STOP=50 for stationary use and START=75 / STOP=80 for general use.

• TLP Project — Battery Care Settings https://linrunner.de/tlp/settings/battery.html Documents valid ranges: START 0–99, STOP 1–100; STOP must exceed START by at least 4.

• Lenovo Support — How to Increase Battery Life https://support.lenovo.com/us/en/solutions/ht078208 Lenovo's official guidance; recommends an 80% charge limit as a general best practice and 40–50% thresholds for machines that are mostly plugged in.

• Arch Linux Wiki — TLP https://wiki.archlinux.org/title/TLP Community-maintained reference with configuration examples aligned with TLP docs.

Travel Prep Note

0 / 100 disables thresholds entirely (charges to 100%). Use this before a long trip, then switch back to Balanced or Desk Mode when you return and plug back in. The 3-second feedback delay in the UI is intentional — writes via batctl complete quickly, but sysfs takes a moment to reflect the new values.