diff --git a/src/arch/avr/i2c.c b/src/arch/avr/i2c.c
index 0ee788b..eb00faa 100644
--- a/src/arch/avr/i2c.c
+++ b/src/arch/avr/i2c.c
@@ -7,7 +7,7 @@
 
 #define TIMEOUT (F_CPU/1000)
 
-int i2c_start(uint8_t addr, bool read) {
+int i2c_start(struct I2C * i2c, uint8_t addr, bool read) {
 	uint32_t count;
 
 	// reset TWI control register
@@ -38,12 +38,12 @@ int i2c_start(uint8_t addr, bool read) {
 	return 0;
 }
 
-void i2c_stop(void) {
+void i2c_stop(struct I2C * i2c) {
 	// transmit STOP condition
 	TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
 }
 
-int i2c_write(uint8_t * data, int length) {
+int i2c_write(struct I2C * i2c, uint8_t * data, int length) {
 	int i;
 	for (i = 0; i < length; i++) {
 		// load data into data register
@@ -62,7 +62,7 @@ int i2c_write(uint8_t * data, int length) {
 	return i;
 }
 
-int i2c_read(uint8_t * data, int length) {
+int i2c_read(struct I2C * i2c, uint8_t * data, int length) {
 	int i;
 	for (i = 0; i < length; i++) {
 	    if ((i + 1) < length) {
diff --git a/src/board/arduino/mega2560/battery.c b/src/board/arduino/mega2560/battery.c
index 484cf29..20be078 100644
--- a/src/board/arduino/mega2560/battery.c
+++ b/src/board/arduino/mega2560/battery.c
@@ -3,11 +3,11 @@
 #include <common/i2c.h>
 
 int smbus_read(uint8_t address, uint8_t command, uint16_t * data) {
-    return i2c_get(address, command, (uint8_t *)data, 2);
+    return i2c_get(NULL, address, command, (uint8_t *)data, 2);
 }
 
 int smbus_write(uint8_t address, uint8_t command, uint16_t data) {
-    return i2c_set(address, command, (uint8_t *)&data, 2);
+    return i2c_set(NULL, address, command, (uint8_t *)&data, 2);
 }
 
 void battery_debug(void) {
diff --git a/src/board/arduino/uno/battery.c b/src/board/arduino/uno/battery.c
index 484cf29..20be078 100644
--- a/src/board/arduino/uno/battery.c
+++ b/src/board/arduino/uno/battery.c
@@ -3,11 +3,11 @@
 #include <common/i2c.h>
 
 int smbus_read(uint8_t address, uint8_t command, uint16_t * data) {
-    return i2c_get(address, command, (uint8_t *)data, 2);
+    return i2c_get(NULL, address, command, (uint8_t *)data, 2);
 }
 
 int smbus_write(uint8_t address, uint8_t command, uint16_t data) {
-    return i2c_set(address, command, (uint8_t *)&data, 2);
+    return i2c_set(NULL, address, command, (uint8_t *)&data, 2);
 }
 
 void battery_debug(void) {