When it negotiates the power draw with the supply unit, and the power supply unit cannot provide the 1.5A at minimum 4.4-4.5V voltage, The Macbook discontinues its power draw. What about lower current chargers or portable batteries? It appears the Macbook typically attempts to draw at least 1.5A from its power supply. When watching a B&W movie in full screen mode, the 10W charger still provides enough power to charge the Macbook at a rate of 0.054 mAh per second, equivalent to a full charge in 27 hours. Thus a total charge would take about 6.5 hours (likely more due to the current drop-off near full charge). When charged with a 10W Apple charger, the Macbook draws 1.8A at 4.61V in my set-up, and reports a charge of 0.23mAh per second of charge in sleep mode. In sleep mode, the 12W charger is able to charge the notebook in about 4-5hrs. In summary, a 5V/2.4A (12W) charger can keep a Macbook 12" operating continuously, charging it at the same time in slightly less than one day. Thus, a total charge would take approximately 4 hours (likely a bit more, due to the current drop-off when the battery is almost full). With the Macbook being folded shut (i.e., sleep mode) and at 70-80% battery capacity, the Macbook reports a charge of 0.36mAh per second. Meanwhile, the Macbook (Coconut Battery) reports a slight charge while in operation (playing a B&W movie) amounting to 0.077mAh per second, equivalent to a full charge in 19+ hours. Using an Orico charger with 2.4A (nominal) "Supercharger" port, and IOGEAR USB-A to USB-C charge cable (3.3ft), I record a power draw of 2.60A with a voltage of 4.72V (voltage drops from nominal 5.00 due to the strong draw). Please ignore my earlier post, as I re-measured many of my earlier data points. For anyone interested in the details of Macbook 12" charging via 5V USB, here some data points ( revised).
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