Editing Macintosh Portable (section)

=== Power system ===
The Portable runs from its main battery, and the adapter charges that battery. The power manager (PMGR) chip on the logic board controls power, sleep and charging and holds the 128 bytes of PRAM.<ref name="ss" /><ref name="tn">TinkerDifferent forum thread [https://tinkerdifferent.com/threads/portable-and-powerbook-100-technical-note-pram-backlight-and-rom-diff.4995/ "Portable and PowerBook 100 Technical Note: PRAM, Backlight, and ROM Diff"], David Cook, January 2026. 128 bytes of PRAM held in the Power Manager; supported PRAM ranges; detecting the backlit model; identical ROM in both models. Secondary source.</ref> Low End Mac warns that the hard disk will not spin up without a charged battery fitted, and that a battery discharged below 5.4 V becomes unusable.<ref name="lembl" /> A switch at the battery cover connects the logic board to the main battery when the cover is fitted and to the 9 V backup battery when it is off, and both power wires to logic board connector J17 are joined in Apple's harness.<ref name="cook" /> Apple warns that leaving the battery cover off with the main battery out keeps power on the logic board, so modules removed or fitted in that state can be damaged.<ref name="ss" />

On the M5120, a separate hybrid module on the logic board provides the always-on 5 V rail, switches the 12 V and −5 V supplies, charges the battery and cuts the machine off at low battery voltage. Androda, who made a replacement, describes the originals as failing from capacitor leakage and from cracked coatings on their trimmed resistors.<ref name="hybrid">TinkerDifferent forum thread [https://tinkerdifferent.com/threads/recreating-macintosh-portable-hybrid-module.899/ "Recreating Macintosh Portable Hybrid Module"], Androda, February-March 2022. Functions of the hybrid module and its failure modes. Secondary source.</ref> The M5126 has the same circuit built directly on the logic board, next to capacitors around the keyboard and trackball connector.<ref name="gotchas" />