More correct algorithm for calculating battery percent

src/Sensors/BatteryController.hpp

@@ -11,7 +11,7 @@ public:
         _battery_data_switch_pin = battery_data_switch_pin;
     }
 
-    void initialize() {
+    void initialize() const {
         pinMode(_battery_data_switch_pin, OUTPUT);
         digitalWrite(_battery_data_switch_pin, HIGH);
         analogReadResolution(12);
@@ -19,19 +19,21 @@ public:
         adcAttachPin(_battery_pin);
     }
 
-    float measureVoltage() {
-        return analogRead(BATTERY_DATA_PIN) * 3.3f / 4096.f;
-    }
-
     int percent(const float minVoltage = 7.2f, const float maxVoltage = 8.4f,
-                const float r1 = 3.3f, const float r2 = 2.f, const float k = 2.87f) {
-        auto batteryVoltage = measureVoltage() * ((r1 + r2) / k);
-        auto percent = ((batteryVoltage - minVoltage) / (maxVoltage - minVoltage)) * 100;
-        return constrain(round(percent), 0, 100);
+                const float r1 = 3.f, const float r2 = 2.f, const float k = 2.85f) {
+        // It's magic. I will return and refactor it.
+        float pinVoltage = analogReadMilliVolts(_battery_pin) / 1000.f;
+        // k = (r1 + r2) / r2
+        float batteryVoltage = pinVoltage * k;
+        return constrain(_map(batteryVoltage, minVoltage, maxVoltage, 0, 100), 0, 100);
     }
 
 private:
     uint16_t _battery_pin;
     uint16_t _battery_data_switch_pin;
     static constexpr const char *_tag = "BatteryController";
+
+    static float _map(float x, float in_min, float in_max, float out_min, float out_max) {
+        return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+    }
 };