AP_BattMonitor: correct Maxell capacity

libraries/AP_BattMonitor/AP_BattMonitor_SMBus.cpp

@@ -54,7 +54,7 @@ bool AP_BattMonitor_SMBus::read_full_charge_capacity(void)
     if (_full_charge_capacity != 0) {
         return true;
     } else if (read_word(BATTMONITOR_SMBUS_FULL_CHARGE_CAPACITY, data)) {
-        _full_charge_capacity = data;
+        _full_charge_capacity = data * get_capacity_scaler();
         return true;
     }
     return false;
@@ -70,7 +70,7 @@ bool AP_BattMonitor_SMBus::read_remaining_capacity(void)
     if (capacity > 0) {
         uint16_t data;
         if (read_word(BATTMONITOR_SMBUS_REMAINING_CAPACITY, data)) {
-            _state.consumed_mah = MAX(0, capacity - data);
+            _state.consumed_mah = MAX(0, capacity - (data * get_capacity_scaler()));
             return true;
         }
     }

libraries/AP_BattMonitor/AP_BattMonitor_SMBus.h

@@ -65,6 +65,9 @@ protected:
     // we know the full charge capacity
     bool read_remaining_capacity(void);
 
+    // return a scaler that should be multiplied by the battery's reported capacity numbers to arrive at the actual capacity in mAh
+    virtual uint16_t get_capacity_scaler() const { return 1; }
+
     // reads the temperature word from the battery
     // returns true if the read was successful
     bool read_temp(void);

libraries/AP_BattMonitor/AP_BattMonitor_SMBus_Maxell.h

@@ -6,4 +6,9 @@ class AP_BattMonitor_SMBus_Maxell : public AP_BattMonitor_SMBus_Generic
 {
     using AP_BattMonitor_SMBus_Generic::AP_BattMonitor_SMBus_Generic;
 
+private:
+
+    // return a scaler that should be multiplied by the battery's reported capacity numbers to arrive at the actual capacity in mAh
+    uint16_t get_capacity_scaler() const override { return 2; }
+
 };