diff --git a/main.c b/main.c
index d7f6aee..f8f454e 100644
--- a/main.c
+++ b/main.c
@@ -26,6 +26,7 @@
 #define BUTTON_CONFIRMATION_BLINK_DURATION_MS 50U
 #define GLOW_BRIGHTNESS_MIN 10U
 #define GLOW_BRIGHTNESS_MAX 100U
+#define INTERNAL_VREF_MV 1024UL
 
 /** Convert milliseconds to system ticks */
 #define MS_TO_TICKS(ms) ((ms) / MAIN_LOOP_SLEEP)
@@ -75,14 +76,14 @@ int main(void)
     VPORTA.DIR &= ~BUTTON_PIN_MASK;    // Input
     PORTA.PIN0CTRL = PORT_PULLUPEN_bm; // Pull-up enabled
 
-    leds_off();                // Ensure all LEDs off at startup
-    battery_level_indicator(); // TODO: Implement
+    leds_off(); // Ensure all LEDs off at startup
 
     bool bLedEnabledOld = bLedEnabled;
     eModeCurrent = ANIMATION_BLINK; // Set the mode to start with
 
     while (true)
     {
+        battery_level_indicator();
         bBtnPressed = handleSwitch(); // Check switch state
 
         // Light LEDs while button is pressed
@@ -162,6 +163,7 @@ static inline void switchMode(void)
  */
 static void configureLowPower(void)
 {
+    return;
     // Set unused pins as outputs LOW to prevent floating inputs
     // Floating inputs can cause extra current consumption
     PORTA.DIRSET = PIN4_bm | PIN5_bm; // Set PA4, PA5 as outputs if unused
@@ -248,13 +250,93 @@ static inline void leds_on(void)
     setPWM_PA2(255U);
 }
 
+/**
+ * @brief Read battery voltage using internal 1.1V reference
+ * @return Estimated battery voltage in millivolts
+ */
+uint16_t readBatteryVoltage(void)
+{
+    // Enable ADC with proper configuration
+    ADC0.CTRLC = ADC_REFSEL_VDDREF_gc | // VCC as reference
+                 ADC_PRESC_DIV4_gc;     // Prescaler DIV4
+
+    // 10-bit resolution (default)
+    ADC0.CTRLA = ADC_RESSEL_10BIT_gc;
+
+    // Select internal voltage reference as input to measure
+    ADC0.MUXPOS = ADC_MUXPOS_INTREF_gc;
+
+    // Enable ADC
+    ADC0.CTRLA |= ADC_ENABLE_bm;
+
+    // Wait for ADC to stabilize
+    _delay_us(100);
+
+    // Dummy conversion for stability
+    ADC0.COMMAND = ADC_STCONV_bm;
+    while (!(ADC0.INTFLAGS & ADC_RESRDY_bm))
+        ;
+    ADC0.INTFLAGS = ADC_RESRDY_bm; // Clear flag
+
+    // Actual conversion
+    ADC0.COMMAND = ADC_STCONV_bm;
+    while (!(ADC0.INTFLAGS & ADC_RESRDY_bm))
+        ;
+
+    uint16_t adcResult = ADC0.RES;
+
+    // Disable ADC to save power
+    ADC0.CTRLA |= !ADC_ENABLE_bm;
+
+    // Check for valid reading
+    if (adcResult == 0 || adcResult >= 1023)
+    {
+        return 0; // Invalid reading
+    }
+
+    // Calculate VCC: V_VCC = VREF × 1023 / ADC_result
+    uint32_t voltage_mv = (INTERNAL_VREF_MV * 1023 / adcResult);
+
+    return (uint16_t)voltage_mv;
+}
+
 /**
  * @brief Battery monitoring
  */
 static void battery_level_indicator(void)
 {
-    // TODO: Implement
-    VPORTA.OUT |= (PA6_SET_MASK | PA7_SET_MASK); // green + red OFF
+    uint16_t voltage = readBatteryVoltage();
+
+    // 1S LiPo voltage ranges:
+    // Good: >=3700mV
+    // Low:  >=3500mV --> 
+
+    // VPORTA.OUT &= ~(PA6_SET_MASK | PA7_SET_MASK); // Turn off both LEDs first
+    VPORTA.OUT |= (PA6_SET_MASK | PA7_SET_MASK); // Red Debug ON
+
+    if (voltage <= 65534)
+    {
+        // Green OFF, Red ON - Low battery
+        //VPORTA.OUT &= ~PA7_SET_MASK; // Red Debug OFF
+    }
+
+    return;
+
+    if (voltage >= 3700)
+    {
+        // Green ON, Red OFF - Good battery
+        VPORTA.OUT &= ~PA6_SET_MASK; // Green ON (active low)
+    }
+    else if (voltage >= 3500)
+    {
+        // Both ON (yellow/orange) - Medium battery
+        VPORTA.OUT &= ~(PA6_SET_MASK | PA7_SET_MASK);
+    }
+    else
+    {
+        // Green OFF, Red ON - Low battery
+        VPORTA.OUT &= ~PA7_SET_MASK; // Red ON (active low)
+    }
 }
 
 /**