diff --git a/EPD/EPD_driver.c b/EPD/EPD_driver.c
index 25967f6..1e837b3 100644
--- a/EPD/EPD_driver.c
+++ b/EPD/EPD_driver.c
@@ -244,7 +244,7 @@ void EPD_LED_BLINK(void) {
     }
 }
 
-float EPD_ReadVoltage(void) {
+uint16_t EPD_ReadVoltage(void) {
 #if defined(S112)
     volatile int16_t value = 0;
     NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_10bit;
@@ -286,7 +286,7 @@ float EPD_ReadVoltage(void) {
     NRF_ADC->ENABLE = 0;
 #endif
     NRF_LOG_DEBUG("ADC value: %d\n", value);
-    return (value * 3.6) / (1 << 10);
+    return (value * 3600) / (1 << 10);
 }
 
 // EPD models
diff --git a/EPD/EPD_driver.h b/EPD/EPD_driver.h
index 97e3904..2cd4b11 100644
--- a/EPD/EPD_driver.h
+++ b/EPD/EPD_driver.h
@@ -218,7 +218,7 @@ void EPD_LED_Toggle(void);
 void EPD_LED_BLINK(void);
 
 // VDD voltage
-float EPD_ReadVoltage(void);
+uint16_t EPD_ReadVoltage(void);
 
 epd_model_t* epd_init(epd_model_id_t id);
 
diff --git a/GUI/GUI.c b/GUI/GUI.c
index 65cdada..b9fe13e 100644
--- a/GUI/GUI.c
+++ b/GUI/GUI.c
@@ -129,12 +129,26 @@ static void DrawTimeSyncTip(Adafruit_GFX* gfx, gui_data_t* data) {
     GFX_printf(gfx, url);
 }
 
-static void DrawBattery(Adafruit_GFX* gfx, int16_t x, int16_t y, uint8_t iw, float voltage) {
+static uint8_t batt_cal(uint16_t voltage) {
+    uint16_t adc_sample = (voltage * 2047) / 3600;
+    if (adc_sample > 1705)
+        return 100;
+    else if (adc_sample <= 1705 && adc_sample > 1584)
+        return 28 + (uint8_t)(((((adc_sample - 1584) << 16) / (1705 - 1584)) * 72) >> 16);
+    else if (adc_sample <= 1584 && adc_sample > 1360)
+        return 4 + (uint8_t)(((((adc_sample - 1360) << 16) / (1584 - 1360)) * 24) >> 16);
+    else if (adc_sample <= 1360 && adc_sample > 1136)
+        return (uint8_t)(((((adc_sample - 1136) << 16) / (1360 - 1136)) * 4) >> 16);
+    else
+        return 0;
+}
+
+static void DrawBattery(Adafruit_GFX* gfx, int16_t x, int16_t y, uint8_t iw, uint16_t voltage) {
     x -= iw;
-    uint8_t level = (uint8_t)(voltage * 100 / 3.6f);
+    uint8_t level = batt_cal(voltage);
     GFX_setFont(gfx, u8g2_font_wqy9_t_lunar);
     GFX_setCursor(gfx, x - GFX_getUTF8Width(gfx, "3.2V") - 2, y + 9);
-    GFX_printf(gfx, "%.1fV", voltage);
+    GFX_printf(gfx, "%d.%dV", voltage / 1000, (voltage % 1000) / 100);
     GFX_fillRect(gfx, x, y, iw, 10, GFX_WHITE);
     GFX_drawRect(gfx, x, y, iw, 10, GFX_BLACK);
     GFX_fillRect(gfx, x + iw, y + 4, 2, 2, GFX_BLACK);
diff --git a/GUI/GUI.h b/GUI/GUI.h
index fec92f3..33e261d 100644
--- a/GUI/GUI.h
+++ b/GUI/GUI.h
@@ -17,7 +17,7 @@ typedef struct {
     uint32_t timestamp;
     uint8_t week_start;  // 0: Sunday, 1: Monday
     int8_t temperature;
-    float voltage;
+    uint16_t voltage;
     char ssid[20];
 } gui_data_t;
 
diff --git a/emulator.c b/emulator.c
index 36f2548..f09efc0 100644
--- a/emulator.c
+++ b/emulator.c
@@ -225,7 +225,7 @@ LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
                 .timestamp = g_display_time,
                 .week_start = g_week_start,
                 .temperature = 25,
-                .voltage = 3.2f,
+                .voltage = 2920,
                 .ssid = "NRF_EPD_84AC",
             };