diff --git a/Inc/config.h b/Inc/config.h
index fad7b88..6ddd017 100644
--- a/Inc/config.h
+++ b/Inc/config.h
@@ -8,6 +8,10 @@
 
 #define DC_CUR_LIMIT     15         // Motor DC current limit in amps. it does not disable motors, it is a soft current limit.
 
+// Battery voltage calibration: connect power source. use multimeter to measure real voltage and write it to BAT_CALIB_REAL_VOLTAGE. watch UART on one of the sensor board cables. write value nr 4 to BAT_CALIB_ADC. make and flash firmware. you can verify voltage on UART debug value 5 (devide it by 100.0 to get calibrated voltage). 
+#define BAT_CALIB_REAL_VOLTAGE        42.0       // input voltage measured by multimeter  
+#define BAT_CALIB_ADC                 1667       // adc-value measured by mainboard (value nr 4 on UART debug output)
+
 #define BAT_LOW_LVL1     36.0       // gently beeps at this voltage level. ~3.6V/cell
 #define BAT_LOW_LVL2     33.0       // your battery is almost empty. Charge now! ~3.3V/cell
 #define BAT_LOW_DEAD     31.0       // undervoltage lockout. ~3.1V/cell
diff --git a/Inc/defines.h b/Inc/defines.h
index 93c17c6..7bda19a 100644
--- a/Inc/defines.h
+++ b/Inc/defines.h
@@ -123,8 +123,7 @@
 
 #define DELAY_TIM_FREQUENCY_US 1000000
 
-#define MOTOR_AMP_CONV_DC_AMP 0.02
-#define ADC_BATTERY_VOLT      0.02647435897435897435897435897436
+#define MOTOR_AMP_CONV_DC_AMP 0.02  // A per bit (12) on ADC.
 
 #define MILLI_R (R * 1000)
 #define MILLI_PSI (PSI * 1000)
diff --git a/Src/bldc.c b/Src/bldc.c
index fb5d1af..0560cdf 100644
--- a/Src/bldc.c
+++ b/Src/bldc.c
@@ -161,8 +161,8 @@ void DMA1_Channel1_IRQHandler() {
     return;
   }
 
-  if (buzzerTimer % 100 == 0) {
-    batteryVoltage = batteryVoltage * 0.999 + ((float)adc_buffer.batt1 * ADC_BATTERY_VOLT) * 0.001;
+  if (buzzerTimer % 100 == 0) {  // because you get float rounding errors if it would run every time
+    batteryVoltage = batteryVoltage * 0.999 + ((float)adc_buffer.batt1 * ((float)BAT_CALIB_REAL_VOLTAGE / (float)BAT_CALIB_ADC)) * 0.001;
   }
 
 
diff --git a/Src/main.c b/Src/main.c
index c36b837..d775fb0 100644
--- a/Src/main.c
+++ b/Src/main.c
@@ -217,8 +217,8 @@ int main(void) {
     #endif
     setScopeChannel(2, (int)speedR);
     setScopeChannel(3, (int)speedL);
-    // setScopeChannel(4, (int));
-    // setScopeChannel(5, (int));
+    setScopeChannel(4, (int)adc_buffer.batt1);  // for battery voltage calibration
+    setScopeChannel(5, (int)(batteryVoltage * 100.0f));  // for verifying battery voltage calibration
     // setScopeChannel(6, (int));
     // setScopeChannel(7, (int));