电量计节点中有capacity_level 节点，这个是反应当前电池电流高低水平的参数。
分为critical low full normal
一般是由fg的芯片来判断，通过IIC读取，具体判断可参考：
case POWER_SUPPLY_PROP_CAPACITY_LEVEL:
if (battery->state & ACPI_BATTERY_STATE_CRITICAL)
val->intval = POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL;
else if (test_bit(ACPI_BATTERY_ALARM_PRESENT, &battery->flags) &&
(battery->capacity_now <= battery->alarm))
val->intval = POWER_SUPPLY_CAPACITY_LEVEL_LOW;
else if (acpi_battery_is_charged(battery))
val->intval = POWER_SUPPLY_CAPACITY_LEVEL_FULL;
else
val->intval = POWER_SUPPLY_CAPACITY_LEVEL_NORMAL;
break;