Add battery indicator, fix display

- Add battery icon with percentage display on main screen
- Implement battery voltage reading via ADC pin 4
- Remove network ID from main display to reduce clutter
- Reorganize UI layout for better space utilization:
  * Move battery icon to prevent text overflow
  * Compact header to single device info line
  * Gain 10 pixels vertical space for device list
- Battery updates every 30 seconds to conserve power
- Network ID still visible on 2-second startup screen

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/config/config.h

@@ -7,6 +7,7 @@
 #define IO_TXD2 17
 #define I2C_SDA 39
 #define I2C_SCL 38
+#define BAT_PIN 4
 
 // UWB Configuration
 #ifndef UWB_INDEX
@@ -26,6 +27,7 @@
 #define DISPLAY_UPDATE_INTERVAL 500
 #define DEVICE_TIMEOUT 5000
 #define SLEEP_DURATION 5000
+#define BATTERY_UPDATE_INTERVAL 30000
 
 // Display Configuration
 #define SCREEN_WIDTH 128

src/main.cpp

@@ -15,6 +15,8 @@ void checkTimeouts();
 void processAnchorBehavior();
 void processTagBehavior();
 void handleSerialPassthrough();
+void updateBatteryLevel();
+void drawBatteryIcon(int x, int y, int percent);
 
 // Hardware setup
 HardwareSerial uwbSerial(2);
@@ -35,6 +37,9 @@ DeviceData anchors[MAX_ANCHORS];
 String response = "";
 unsigned long lastDisplayUpdate = 0;
 unsigned long lastPositioningUpdate = 0;
+unsigned long lastBatteryUpdate = 0;
+float batteryVoltage = 0.0;
+int batteryPercent = 0;
 
 void setup() {
     Serial.begin(SERIAL_BAUD);
@@ -122,6 +127,9 @@ void setup() {
         }
     #endif
     
+    // Initial battery reading
+    updateBatteryLevel();
+    
     Serial.printf("%s ready! Network ID: %d\n", deviceConfig.deviceName, NETWORK_ID);
     
     #if DEVICE_TYPE == DEVICE_ANCHOR
@@ -155,6 +163,12 @@ void loop() {
     checkTimeouts();
     handleSerialPassthrough();
     
+    // Update battery level periodically
+    if (millis() - lastBatteryUpdate > BATTERY_UPDATE_INTERVAL) {
+        updateBatteryLevel();
+        lastBatteryUpdate = millis();
+    }
+    
     // Execute device-specific behavior
     if (DEVICE_IS_ANCHOR) {
         processAnchorBehavior();
@@ -209,10 +223,14 @@ void updateDisplay() {
     display.setTextSize(1);
     display.setTextColor(SSD1306_WHITE);
     
-    // Header
+    // Header - Device info with battery
     display.setCursor(0, 0);
-    display.printf("%s %d (Net:%d)", deviceConfig.deviceName, deviceConfig.deviceId, NETWORK_ID);
+    display.printf("%s %d", deviceConfig.deviceName, deviceConfig.deviceId);
     
+    // Battery indicator in top right
+    drawBatteryIcon(80, 0, batteryPercent);
+    
+    // Status line
     display.setCursor(0, 10);
     display.println(deviceConfig.statusDisplayPrefix);
     
@@ -375,4 +393,23 @@ void showStartupScreen() {
     delay(2000);
 }
 
+void updateBatteryLevel() {
+    batteryVoltage = 3.3 * analogRead(BAT_PIN) / 4096.0 * 2;
+    batteryPercent = constrain(map((int)(batteryVoltage * 100), 300, 420, 0, 100), 0, 100);
+}
+
+void drawBatteryIcon(int x, int y, int percent) {
+    display.drawRect(x, y, 18, 10, SSD1306_WHITE);
+    display.fillRect(x + 18, y + 3, 2, 4, SSD1306_WHITE);
+    
+    int fillWidth = (14 * percent) / 100;
+    if (fillWidth > 0) {
+        display.fillRect(x + 2, y + 2, fillWidth, 6, SSD1306_WHITE);
+    }
+    
+    display.setCursor(x + 22, y + 1);
+    display.setTextSize(1);
+    display.printf("%d%%", percent);
+}
+
 // Cleanup - no dynamic allocation needed