diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp b/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp
index 728e3b918adca..88b5d1450f74a 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp
@@ -138,9 +138,12 @@ AP_BattMonitor::Failsafe AP_BattMonitor_Backend::update_failsafes(void)
         // this is the first time our voltage has dropped below minimum so start timer
         if (_state.critical_voltage_start_ms == 0) {
             _state.critical_voltage_start_ms = now;
-        } else if (_params._low_voltage_timeout > 0 &&
-                   now - _state.critical_voltage_start_ms > uint32_t(_params._low_voltage_timeout)*1000U) {
-            return AP_BattMonitor::Failsafe::Critical;
+        } else {
+            int32_t voltage_timeout = _params._crt_voltage_timeout > 0 ? _params._crt_voltage_timeout : _params._low_voltage_timeout*1000;
+            if (voltage_timeout > 0 &&
+                now - _state.critical_voltage_start_ms > uint32_t(voltage_timeout)) {
+                return AP_BattMonitor::Failsafe::Critical;
+            }
         }
     } else {
         // acceptable voltage so reset timer
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_Params.cpp b/libraries/AP_BattMonitor/AP_BattMonitor_Params.cpp
index 63d4ebe4d8124..d19871bb3f544 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_Params.cpp
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_Params.cpp
@@ -169,6 +169,17 @@ const AP_Param::GroupInfo AP_BattMonitor_Params::var_info[] = {
     AP_GROUPINFO("ESC_INDEX", 22, AP_BattMonitor_Params, _esc_telem_outbound_index, 0),
 #endif
 
+#ifndef HAL_BUILD_AP_PERIPH
+    // @Param: CRT_TIMER
+    // @DisplayName: Critical voltage timeout
+    // @Description: This is the timeout in milli-seconds before a critical voltage event will be triggered. For aircraft with low C batteries it may be necessary to raise this in order to cope with critical voltage on long takeoffs. A value of zero disables critical voltage errors.
+    // @Units: ms
+    // @Increment: 1
+    // @Range: 0 120000
+    // @User: Advanced
+    AP_GROUPINFO("CRT_TIMER", 23, AP_BattMonitor_Params, _crt_voltage_timeout, 0),
+#endif // HAL_BUILD_AP_PERIPH
+
     AP_GROUPEND
 
 };
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_Params.h b/libraries/AP_BattMonitor/AP_BattMonitor_Params.h
index 4665e0eeaa46a..3dd36fb6d07be 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_Params.h
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_Params.h
@@ -46,6 +46,7 @@ class AP_BattMonitor_Params {
 #endif
     AP_Int8  _type;                     /// 0=disabled, 3=voltage only, 4=voltage and current
     AP_Int8  _low_voltage_timeout;      /// timeout in seconds before a low voltage event will be triggered
+    AP_Int32 _crt_voltage_timeout;      /// timeout in milli-seconds before a critical voltage event will be triggered
     AP_Int8  _failsafe_voltage_source;  /// voltage type used for detection of low voltage event
     AP_Int8  _failsafe_low_action;      /// action to preform on a low battery failsafe
     AP_Int8  _failsafe_critical_action; /// action to preform on a critical battery failsafe