The PBT_APMBATTERYLOW message is sent to notify applications that battery power is low. A window receives this message through the WM_POWERBROADCAST message.
PBT_APMBATTERYLOW dwData = (DWORD) lParam;
No return value.
This message is broadcast when a system’s APM BIOS signals an APM battery low notification. Because some APM BIOS implementations do not provide battery low notifications, this message may never be sent on some machines.