Fixes maintainer requests

lib/hal/HalGPIO.cpp

@@ -1,5 +1,6 @@
 #include <HalGPIO.h>
 #include <SPI.h>
+#include <Wire.h>
 #include <esp_sleep.h>
 
 void HalGPIO::begin() {
@@ -14,6 +15,16 @@ void HalGPIO::begin() {
 
   pinMode(_batteryPin, INPUT);
   pinMode(UART0_RXD, INPUT);
+
+  // I2C init must come AFTER pinMode(UART0_RXD) because GPIO20 is shared
+  // between USB detection (digital read) and I2C SDA. Wire.begin()
+  // reconfigures the pin for I2C, so it must run last.
+  if (_deviceType == DeviceType::X3) {
+    Wire.begin(20, 0, 400000);
+    _useI2C = true;
+    _i2cAddr = 0x55;
+    _socRegister = 0x2C;
+  }
 }
 
 void HalGPIO::update() { inputMgr.update(); }
@@ -43,8 +54,18 @@ void HalGPIO::startDeepSleep() {
 }
 
 int HalGPIO::getBatteryPercentage() const {
-  if (_deviceType == DeviceType::X3) {
-    return 0;
+  if (_useI2C) {
+    // Read SOC directly from I2C fuel gauge (16-bit LE register).
+    // Returns 0 on I2C error so the UI shows 0% rather than crashing.
+    Wire.beginTransmission(_i2cAddr);
+    Wire.write(_socRegister);
+    if (Wire.endTransmission(false) != 0) return 0;
+    Wire.requestFrom(_i2cAddr, (uint8_t)2);
+    if (Wire.available() < 2) return 0;
+    const uint8_t lo = Wire.read();
+    const uint8_t hi = Wire.read();
+    const uint16_t soc = (hi << 8) | lo;
+    return soc > 100 ? 100 : soc;
   }
   static const BatteryMonitor bat(BAT_GPIO0);
   return bat.readPercentage();