AP_BattMonitor_Backend: change capacity_remaining_pct() to a bool

libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp

@@ -30,15 +30,16 @@ AP_BattMonitor_Backend::AP_BattMonitor_Backend(AP_BattMonitor &mon, AP_BattMonit
 {
 }
 
-/// capacity_remaining_pct - returns the % battery capacity remaining (0 ~ 100)
-uint8_t AP_BattMonitor_Backend::capacity_remaining_pct() const
+/// capacity_remaining_pct - returns true if the battery % is available and writes to the percentage argument
+bool AP_BattMonitor_Backend::capacity_remaining_pct(uint8_t &percentage) const
 {
-    float mah_remaining = _params._pack_capacity - _state.consumed_mah;
-    if ( _params._pack_capacity > 10 ) { // a very very small battery
-        return MIN(MAX((100 * (mah_remaining) / _params._pack_capacity), 0), UINT8_MAX);
-    } else {
-        return 0;
+    // we consider anything under 10 mAh as being an invalid capacity and so will be our measurement of remaining capacity
+    if ( _params._pack_capacity <= 10) {
+        return false;
     }
+    const float mah_remaining = _params._pack_capacity - _state.consumed_mah;
+    percentage = constrain_float(100 * mah_remaining / _params._pack_capacity, 0, UINT8_MAX);
+    return true;
 }
 
 // update battery resistance estimate

libraries/AP_BattMonitor/AP_BattMonitor_Backend.h

@@ -46,8 +46,8 @@ public:
     // returns true if battery monitor provides temperature
     virtual bool has_temperature() const { return false; }
 
-    /// capacity_remaining_pct - returns the % battery capacity remaining (0 ~ 100)
-    virtual uint8_t capacity_remaining_pct() const;
+    /// capacity_remaining_pct - returns true if the percentage is valid and writes to percentage argument
+    virtual bool capacity_remaining_pct(uint8_t &percentage) const WARN_IF_UNUSED;
 
     // return true if cycle count can be provided and fills in cycles argument
     virtual bool get_cycle_count(uint16_t &cycles) const { return false; }