fixes battery reading on x3

lib/hal/HalGPIO.cpp

@@ -44,11 +44,10 @@ void HalGPIO::startDeepSleep() {
 
 int HalGPIO::getBatteryPercentage() const {
   if (_deviceType == DeviceType::X3) {
-    // X3 battery telemetry is not on ADC in stock fw; avoid fighting EPD DC on GPIO4.
     return 0;
   }
-  static const BatteryMonitor battery = BatteryMonitor(BAT_GPIO0);
+  static const BatteryMonitor bat(BAT_GPIO0);
-  return battery.readPercentage();
+  return bat.readPercentage();
 }
 
 bool HalGPIO::isUsbConnected() const {

src/Battery.cpp

@@ -0,0 +1,9 @@
+#include "Battery.h"
+
+// Meyer's singleton — guaranteed single instance across all translation units.
+// Constructed with GPIO0 (X4 ADC default). For X3, main.cpp calls
+// battery().setI2CFuelGauge() to switch to BQ27220 I2C reads instead.
+BatteryMonitor& battery() {
+  static BatteryMonitor instance(BAT_GPIO0);
+  return instance;
+}

src/Battery.h

@@ -1,6 +1,11 @@
 #pragma once
 #include <BatteryMonitor.h>
 
-#define BAT_GPIO0 0  // Battery voltage
+#define BAT_GPIO0 0  // Battery voltage (X4 ADC pin)
 
-static BatteryMonitor battery(BAT_GPIO0);
+// Shared battery monitor singleton. Returns a single BatteryMonitor instance
+// used by all callers (themes, activities, etc.).
+//
+// - X4: reads battery voltage via ADC on GPIO0 (default, no extra setup needed)
+// - X3: reads SOC from BQ27220 fuel gauge via I2C (call setI2CFuelGauge() after Wire.begin())
+BatteryMonitor& battery();

src/components/themes/BaseTheme.cpp

@@ -22,7 +22,7 @@ constexpr int homeMarginTop = 30;
 void BaseTheme::drawBattery(const GfxRenderer& renderer, Rect rect, const bool showPercentage) const {
   // Left aligned battery icon and percentage
   // TODO refactor this so the percentage doesnt change after we position it
-  const uint16_t percentage = battery.readPercentage();
+  const uint16_t percentage = battery().readPercentage();
   if (showPercentage) {
     const auto percentageText = std::to_string(percentage) + "%";
     renderer.drawText(SMALL_FONT_ID, rect.x + batteryPercentSpacing + BaseMetrics::values.batteryWidth, rect.y,
@@ -232,7 +232,7 @@ void BaseTheme::drawHeader(const GfxRenderer& renderer, Rect rect, const char* t
       SETTINGS.hideBatteryPercentage != CrossPointSettings::HIDE_BATTERY_PERCENTAGE::HIDE_ALWAYS;
   int batteryX = rect.x + rect.width - BaseMetrics::values.contentSidePadding - BaseMetrics::values.batteryWidth;
   if (showBatteryPercentage) {
-    const uint16_t percentage = battery.readPercentage();
+    const uint16_t percentage = battery().readPercentage();
     const auto percentageText = std::to_string(percentage) + "%";
     batteryX -= renderer.getTextWidth(SMALL_FONT_ID, percentageText.c_str());
   }

src/components/themes/lyra/LyraTheme.cpp

@@ -22,7 +22,7 @@ constexpr int topHintButtonY = 345;
 
 void LyraTheme::drawBattery(const GfxRenderer& renderer, Rect rect, const bool showPercentage) const {
   // Left aligned battery icon and percentage
-  const uint16_t percentage = battery.readPercentage();
+  const uint16_t percentage = battery().readPercentage();
   if (showPercentage) {
     const auto percentageText = std::to_string(percentage) + "%";
     renderer.drawText(SMALL_FONT_ID, rect.x + batteryPercentSpacing + LyraMetrics::values.batteryWidth, rect.y,
@@ -64,7 +64,7 @@ void LyraTheme::drawHeader(const GfxRenderer& renderer, Rect rect, const char* t
       SETTINGS.hideBatteryPercentage != CrossPointSettings::HIDE_BATTERY_PERCENTAGE::HIDE_ALWAYS;
   int batteryX = rect.x + rect.width - LyraMetrics::values.contentSidePadding - LyraMetrics::values.batteryWidth;
   if (showBatteryPercentage) {
-    const uint16_t percentage = battery.readPercentage();
+    const uint16_t percentage = battery().readPercentage();
     const auto percentageText = std::to_string(percentage) + "%";
     batteryX -= renderer.getTextWidth(SMALL_FONT_ID, percentageText.c_str());
   }

src/main.cpp

@@ -5,6 +5,7 @@
 #include <HalGPIO.h>
 #include <HalStorage.h>
 #include <SPI.h>
+#include <Wire.h>
 #include <builtinFonts/all.h>
 
 #include <cstring>
@@ -259,6 +260,11 @@ void setupDisplayAndFonts() {
     display.setBwOnly(true);
     display.setControllerType(EInkDisplay::ControllerType::SSD1677);
     display.setDisplayDimensions(792, 528);
+    // X3 has a BQ27220 fuel gauge on I2C (addr 0x55) instead of an ADC voltage
+    // divider. SOC (0-100%) is read directly from register 0x2C.
+    // I2C bus: SDA=GPIO20, SCL=GPIO0, 400kHz (matches stock X3 firmware).
+    Wire.begin(20, 0, 400000);
+    battery().setI2CFuelGauge(0x55, 0x2C);
   }
   display.begin();
   renderer.begin();