diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus.h b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus.h
index 33a9432a71..444e1df333 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus.h
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus.h
@@ -7,7 +7,7 @@
 #include <AP_Math.h>
 #include "AP_BattMonitor_Backend.h"
 
-#define AP_BATTMONITOR_SMBUS_MAX_CELLS 4
+#define AP_BATTMONITOR_SMBUS_TIMEOUT_MICROS 5000000    // sensor becomes unhealthy if no successful readings for 5 seconds
 
 class AP_BattMonitor_SMBus : public AP_BattMonitor_Backend
 {
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp
index 0893505484..fa065db92a 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp
@@ -43,6 +43,7 @@ void AP_BattMonitor_SMBus_I2C::read()
     if (read_word(BATTMONITOR_SMBUS_VOLTAGE, data)) {
         _state.voltage = (float)data / 1000.0f;
         _state.last_time_micros = tnow;
+        _state.healthy = true;
     }
 
     // read current
@@ -50,6 +51,11 @@ void AP_BattMonitor_SMBus_I2C::read()
         _state.current_amps = (float)((int32_t)((uint32_t)buff[3]<<24 | (uint32_t)buff[2]<<16 | (uint32_t)buff[1]<<8 | (uint32_t)buff[0])) / 1000.0f;
         _state.last_time_micros = tnow;
     }
+
+    // timeout after 5 seconds
+    if ((tnow - _state.last_time_micros) > AP_BATTMONITOR_SMBUS_TIMEOUT_MICROS) {
+        _state.healthy = false;
+    }
 }
 
 // read word from register
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.cpp b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.cpp
index b75726de75..6ef5e321b2 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.cpp
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.cpp
@@ -55,6 +55,13 @@ void AP_BattMonitor_SMBus_PX4::read()
             _state.voltage = batt_status.voltage_v;
             _state.current_amps = batt_status.current_a;
             _state.last_time_micros = hal.scheduler->micros();
+            _state.current_total_mah = batt_status.discharged_mah;
+            _state.healthy = true;
+        }
+    } else if (_state.healthy) {
+        // timeout after 5 seconds
+        if ((hal.scheduler->micros() - _state.last_time_micros) > AP_BATTMONITOR_SMBUS_TIMEOUT_MICROS) {
+            _state.healthy = false;
         }
     }
 }
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.h b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.h
index e59e0441a6..25dab90da7 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.h
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_PX4.h
@@ -34,7 +34,6 @@ public:
 
 private:
     int         _batt_sub;          // orb subscription description
-    uint64_t    _last_timestamp;    // time of last update (used to avoid processing old reports)
 };
 
 #endif // AP_BATTMONITOR_SMBUS_PX4_H