Advanced Configuration and Power Interface Specification

ACPI Overview
the battery is able to provide, and what the run-time would be at a predetermined rate of
consumption.
3.9.2 Battery Capacity
Each battery must report its designed capacity, latest full-charged capacity, and present remaining
capacity. Remaining capacity decreases during usage, and it also changes depending on the
environment. Therefore, the OS must use latest full-charged capacity to calculate the battery
percentage. In addition the battery system must report warning and low battery levels at which the
user must be notified and the system transitioned to a sleeping state. See Figure 3-4 for the relation
of these five values.
A system may use either rate and capacity [mA/mAh] or power and energy [mW/mWh] for the unit
of battery information calculation and reporting. Mixing [mA] and [mW] is not allowed on a system.
Designed capacity
Last full charged capacity
Present remaining capacity
OEM designed initial capacity for warning
OEM designed initial capacity for low
3.9.3 Battery Gas Gauge
Figure 3-4 Reporting Battery Capacity
At the most basic level, the OS calculates Remaining Battery Percentage [%] using the following
formula:
Battery Remaining Capacity [mAh/mWh]
Remaining Battery Percentage[%] =
Last Full Charged Capacity [mAh/mWh]
* 100
Figure 3-5 Remaining Battery Percent Formula
Control Method Battery also reports the Present Drain Rate [mA or mW] for calculating the remaining battery life. At
the most basic level, Remaining Battery life is calculated by following formula:
Remaining Battery Life [h]=
Battery Remaining Capacity [mAh/mWh]
Battery Present Drain Rate [mA/mW]
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