diff --git a/sys/dev/acpica/acpi_battery.c b/sys/dev/acpica/acpi_battery.c
index dd2b3fa..ba57853 100644
--- a/sys/dev/acpica/acpi_battery.c
+++ b/sys/dev/acpica/acpi_battery.c
@@ -102,8 +102,9 @@ acpi_battery_get_info_expire(void)
 int
 acpi_battery_bst_valid(struct acpi_bst *bst)
 {
-    return (bst->state < ACPI_BATT_STAT_MAX && bst->cap != ACPI_BATT_UNKNOWN &&
-	bst->volt != ACPI_BATT_UNKNOWN);
+
+    return (bst->state != ACPI_BATT_STAT_NOT_PRESENT &&
+	bst->cap != ACPI_BATT_UNKNOWN && bst->volt != ACPI_BATT_UNKNOWN);
 }
 
 /* Check _BIF results for validity. */
diff --git a/sys/dev/acpica/acpi_cmbat.c b/sys/dev/acpica/acpi_cmbat.c
index dde3ad5..6c6525d 100644
--- a/sys/dev/acpica/acpi_cmbat.c
+++ b/sys/dev/acpica/acpi_cmbat.c
@@ -279,6 +279,12 @@ acpi_cmbat_get_bst(void *arg)
 	goto end;
     acpi_cmbat_info_updated(&sc->bst_lastupdated);
 
+    /* Clear out undefined/extended bits that might be set by hardware. */
+    sc->bst.state &= ACPI_BATT_STAT_BST_MASK;
+    if ((sc->bst.state & ACPI_BATT_STAT_INVALID) == ACPI_BATT_STAT_INVALID)
+	ACPI_VPRINT(dev, acpi_device_get_parent_softc(dev),
+	    "battery reports simultaneous charging and discharging\n");
+
     /* XXX If all batteries are critical, perhaps we should suspend. */
     if (sc->bst.state & ACPI_BATT_STAT_CRITICAL) {
     	if ((sc->flags & ACPI_BATT_STAT_CRITICAL) == 0) {
diff --git a/sys/dev/acpica/acpi_smbat.c b/sys/dev/acpica/acpi_smbat.c
index 02a461e..bdaf945 100644
--- a/sys/dev/acpica/acpi_smbat.c
+++ b/sys/dev/acpica/acpi_smbat.c
@@ -390,6 +390,7 @@ acpi_smbat_get_bst(device_t dev, struct acpi_bst *bst)
 
 	if (val > 0) {
 		sc->bst.rate = val * factor;
+		sc->bst.state &= ~SMBATT_BS_DISCHARGING;
 		sc->bst.state |= ACPI_BATT_STAT_CHARGING;
 	} else if (val < 0)
 		sc->bst.rate = (-val) * factor;
diff --git a/sys/dev/acpica/acpiio.h b/sys/dev/acpica/acpiio.h
index f085838..c65028f 100644
--- a/sys/dev/acpica/acpiio.h
+++ b/sys/dev/acpica/acpiio.h
@@ -74,11 +74,22 @@ struct acpi_bst {
     uint32_t volt;			/* Present Voltage */
 };
 
+/*
+ * Note that the following definitions represent status bits for internal
+ * driver state.  The first three of them (charging, discharging and critical)
+ * conveninetly conform to ACPI specification of status returned by _BST
+ * method.  Other definitions (not present, etc) are synthetic.
+ * Also note that according to the specification the charging and discharging
+ * status bits must not be set at the same time.
+ */
 #define ACPI_BATT_STAT_DISCHARG		0x0001
 #define ACPI_BATT_STAT_CHARGING		0x0002
 #define ACPI_BATT_STAT_CRITICAL		0x0004
-#define ACPI_BATT_STAT_NOT_PRESENT	0x0007
-#define ACPI_BATT_STAT_MAX		0x0007
+#define ACPI_BATT_STAT_INVALID					\
+    (ACPI_BATT_STAT_DISCHARG | ACPI_BATT_STAT_CHARGING)
+#define ACPI_BATT_STAT_BST_MASK					\
+    (ACPI_BATT_STAT_INVALID | ACPI_BATT_STAT_CRITICAL)
+#define ACPI_BATT_STAT_NOT_PRESENT	ACPI_BATT_STAT_BST_MASK
 
 union acpi_battery_ioctl_arg {
     int			 unit;	/* Device unit or ACPI_BATTERY_ALL_UNITS. */