diff --git a/sys/x86/isa/atrtc.c b/sys/x86/isa/atrtc.c
--- a/sys/x86/isa/atrtc.c
+++ b/sys/x86/isa/atrtc.c
@@ -62,6 +62,11 @@
 #include <machine/md_var.h>
 #endif
 
+/* tunable to detect a power loss of the rtc */
+static bool atrtc_power_lost = false;
+SYSCTL_BOOL(_machdep, OID_AUTO, atrtc_power_lost, CTLFLAG_RD, &atrtc_power_lost,
+    false, "RTC lost power on last power cycle (probably caused by an emtpy cmos battery)");
+
 /*
  * atrtc_lock protects low-level access to individual hardware registers.
  * atrtc_time_lock protects the entire sequence of accessing multiple registers
@@ -600,6 +605,7 @@
 
 	/* Look if we have a RTC present and the time is valid */
 	if (!(rtcin(RTC_STATUSD) & RTCSD_PWR)) {
+		atrtc_power_lost = true;
 		device_printf(dev, "WARNING: Battery failure indication\n");
 		return (EINVAL);
 	}