diff --git a/BatteryMeter.c b/BatteryMeter.c
index 859df9d7..0ae2834c 100644
--- a/BatteryMeter.c
+++ b/BatteryMeter.c
@@ -15,6 +15,7 @@ This meter written by Ian P. Hands (iphands@gmail.com, ihands@redhat.com).
 #include "StringUtils.h"
 #include "Platform.h"
 
+#include <math.h>
 #include <string.h>
 #include <stdlib.h>
 
@@ -29,8 +30,8 @@ static void BatteryMeter_updateValues(Meter * this, char *buffer, int len) {
 
    Battery_getData(&percent, &isOnAC);
 
-   if (percent == -1) {
-      this->values[0] = 0;
+   if (isnan(percent)) {
+      this->values[0] = NAN;
       xSnprintf(buffer, len, "n/a");
       return;
    }
diff --git a/darwin/Battery.c b/darwin/Battery.c
index d52a5954..51d49c6d 100644
--- a/darwin/Battery.c
+++ b/darwin/Battery.c
@@ -1,6 +1,8 @@
 
 #include "BatteryMeter.h"
 
+#include <math.h>
+
 #include <CoreFoundation/CoreFoundation.h>
 #include <CoreFoundation/CFString.h>
 #include <IOKit/ps/IOPowerSources.h>
@@ -9,7 +11,7 @@
 void Battery_getData(double* level, ACPresence* isOnAC) {
    CFTypeRef power_sources = IOPSCopyPowerSourcesInfo();
 
-   *level = -1;
+   *level = NAN;
    *isOnAC = AC_ERROR;
 
    if(NULL == power_sources) {
diff --git a/dragonflybsd/Battery.c b/dragonflybsd/Battery.c
index f17efb5d..58960429 100644
--- a/dragonflybsd/Battery.c
+++ b/dragonflybsd/Battery.c
@@ -7,13 +7,14 @@ in the source distribution for its full text.
 */
 
 #include "BatteryMeter.h"
+#include <math.h>
 #include <sys/sysctl.h>
 
 void Battery_getData(double* level, ACPresence* isOnAC) {
    int life;
    size_t life_len = sizeof(life);
    if (sysctlbyname("hw.acpi.battery.life", &life, &life_len, NULL, 0) == -1)
-      *level = -1;
+      *level = NAN;
    else
       *level = life;
 
diff --git a/freebsd/Battery.c b/freebsd/Battery.c
index b8c5e312..009f7abe 100644
--- a/freebsd/Battery.c
+++ b/freebsd/Battery.c
@@ -6,13 +6,14 @@ in the source distribution for its full text.
 */
 
 #include "BatteryMeter.h"
+#include <math.h>
 #include <sys/sysctl.h>
 
 void Battery_getData(double* level, ACPresence* isOnAC) {
    int life;
    size_t life_len = sizeof(life);
    if (sysctlbyname("hw.acpi.battery.life", &life, &life_len, NULL, 0) == -1)
-      *level = -1;
+      *level = NAN;
    else
       *level = life;
 
diff --git a/linux/Battery.c b/linux/Battery.c
index 1930880d..f92a3176 100644
--- a/linux/Battery.c
+++ b/linux/Battery.c
@@ -17,6 +17,7 @@ Linux battery readings written by Ian P. Hands (iphands@gmail.com, ihands@redhat
 #include <string.h>
 #include <fcntl.h>
 #include <time.h>
+#include <math.h>
 #include "BatteryMeter.h"
 #include "StringUtils.h"
 
@@ -140,18 +141,18 @@ static ACPresence procAcpiCheck(void) {
 static double Battery_getProcBatData(void) {
    const unsigned long int totalFull = parseBatInfo("info", 3, 4);
    if (totalFull == 0)
-      return 0;
+      return NAN;
 
    const unsigned long int totalRemain = parseBatInfo("state", 5, 3);
    if (totalRemain == 0)
-      return 0;
+      return NAN;
 
    return totalRemain * 100.0 / (double) totalFull;
 }
 
 static void Battery_getProcData(double* level, ACPresence* isOnAC) {
-   *level = Battery_getProcBatData();
    *isOnAC = procAcpiCheck();
+   *level = AC_ERROR != *isOnAC ? Battery_getProcBatData() : NAN;
 }
 
 // ----------------------------------------
@@ -176,7 +177,7 @@ static inline ssize_t xread(int fd, void *buf, size_t count) {
 
 static void Battery_getSysData(double* level, ACPresence* isOnAC) {
 
-   *level = 0;
+   *level = NAN;
    *isOnAC = AC_ERROR;
 
    DIR *dir = opendir(SYS_POWERSUPPLY_DIR);
@@ -279,13 +280,14 @@ static void Battery_getSysData(double* level, ACPresence* isOnAC) {
       }
    }
    closedir(dir);
-   *level = totalFull > 0 ? ((double) totalRemain * 100) / (double) totalFull : 0;
+
+   *level = totalFull > 0 ? ((double) totalRemain * 100.0) / (double) totalFull : NAN;
 }
 
 static enum { BAT_PROC, BAT_SYS, BAT_ERR } Battery_method = BAT_PROC;
 
 static time_t Battery_cacheTime = 0;
-static double Battery_cacheLevel = 0;
+static double Battery_cacheLevel = NAN;
 static ACPresence Battery_cacheIsOnAC = 0;
 
 void Battery_getData(double* level, ACPresence* isOnAC) {
@@ -299,22 +301,21 @@ void Battery_getData(double* level, ACPresence* isOnAC) {
 
    if (Battery_method == BAT_PROC) {
       Battery_getProcData(level, isOnAC);
-      if (*level == 0) {
+      if (isnan(*level)) {
          Battery_method = BAT_SYS;
       }
    }
    if (Battery_method == BAT_SYS) {
       Battery_getSysData(level, isOnAC);
-      if (*level == 0) {
+      if (isnan(*level)) {
          Battery_method = BAT_ERR;
       }
    }
    if (Battery_method == BAT_ERR) {
-      *level = -1;
+      *level = NAN;
       *isOnAC = AC_ERROR;
-   }
-   if (*level > 100.0) {
-      *level = 100.0;
+   } else {
+      CLAMP(*level, 0.0, 100.0);
    }
    Battery_cacheLevel = *level;
    Battery_cacheIsOnAC = *isOnAC;
diff --git a/openbsd/Battery.c b/openbsd/Battery.c
index c215e418..66e4b631 100644
--- a/openbsd/Battery.c
+++ b/openbsd/Battery.c
@@ -10,6 +10,7 @@ in the source distribution for its full text.
 #include <sys/sysctl.h>
 #include <sys/sensors.h>
 #include <errno.h>
+#include <math.h>
 #include <string.h>
 
 static bool findDevice(const char* name, int* mib, struct sensordev* snsrdev, size_t* sdlen) {
@@ -36,7 +37,7 @@ void Battery_getData(double* level, ACPresence* isOnAC) {
 
    bool found = findDevice("acpibat0", mib, &snsrdev, &sdlen);
 
-   *level = -1;
+   *level = NAN;
    if (found) {
       /* last full capacity */
       mib[3] = 7;
diff --git a/solaris/Battery.c b/solaris/Battery.c
index 080cf540..121d2e49 100644
--- a/solaris/Battery.c
+++ b/solaris/Battery.c
@@ -1,7 +1,8 @@
+#include <math.h>
 
 #include "BatteryMeter.h"
 
 void Battery_getData(double* level, ACPresence* isOnAC) {
-   *level = -1;
+   *level = NAN;
    *isOnAC = AC_ERROR;
 }
diff --git a/unsupported/Battery.c b/unsupported/Battery.c
index 080cf540..121d2e49 100644
--- a/unsupported/Battery.c
+++ b/unsupported/Battery.c
@@ -1,7 +1,8 @@
+#include <math.h>
 
 #include "BatteryMeter.h"
 
 void Battery_getData(double* level, ACPresence* isOnAC) {
-   *level = -1;
+   *level = NAN;
    *isOnAC = AC_ERROR;
 }