AP_BattMonitor: Provide the time remaining

libraries/AP_BattMonitor/AP_BattMonitor.cpp

@@ -568,6 +568,16 @@ bool AP_BattMonitor::capacity_remaining_pct(uint8_t &percentage, uint8_t instanc
     return false;
 }
 
+/// time_remaining - returns remaining battery time
+bool AP_BattMonitor::time_remaining(uint32_t &seconds, uint8_t instance) const
+{
+    if (instance < _num_instances && drivers[instance] != nullptr && state[instance].has_time_remaining) {
+        seconds = state[instance].time_remaining;
+        return true;
+    }
+    return false;
+}
+
 /// pack_capacity_mah - returns the capacity of the battery pack in mAh when the pack is full
 int32_t AP_BattMonitor::pack_capacity_mah(uint8_t instance) const
 {

libraries/AP_BattMonitor/AP_BattMonitor.h

@@ -136,6 +136,8 @@ public:
         bool        healthy;                   // battery monitor is communicating correctly
         bool        is_powering_off;           // true when power button commands power off
         bool        powerOffNotified;          // only send powering off notification once
+        uint32_t    time_remaining;            // remaining battery time
+        bool        has_time_remaining;        // time_remaining is only valid if this is true
         const struct AP_Param::GroupInfo *var_info;
     };
 
@@ -177,6 +179,9 @@ public:
     virtual bool capacity_remaining_pct(uint8_t &percentage, uint8_t instance) const WARN_IF_UNUSED;
     bool capacity_remaining_pct(uint8_t &percentage) const WARN_IF_UNUSED { return capacity_remaining_pct(percentage, AP_BATT_PRIMARY_INSTANCE); }
 
+    /// time_remaining - returns remaining battery time
+    bool time_remaining(uint32_t &seconds, const uint8_t instance = AP_BATT_PRIMARY_INSTANCE) const WARN_IF_UNUSED;
+
     /// pack_capacity_mah - returns the capacity of the battery pack in mAh when the pack is full
     int32_t pack_capacity_mah(uint8_t instance) const;
     int32_t pack_capacity_mah() const { return pack_capacity_mah(AP_BATT_PRIMARY_INSTANCE); }

libraries/AP_BattMonitor/AP_BattMonitor_Backend.h

@@ -34,6 +34,9 @@ public:
     // read the latest battery voltage
     virtual void read() = 0;
 
+    /// returns true if battery monitor instance provides time remaining info
+    virtual bool has_time_remaining() const { return false; }
+
     /// returns true if battery monitor instance provides consumed energy info
     virtual bool has_consumed_energy() const { return false; }