diff --git a/oepl-definitions.h b/oepl-definitions.h
index c6ec9155..60961f4b 100755
--- a/oepl-definitions.h
+++ b/oepl-definitions.h
@@ -131,6 +131,7 @@
 #define CMD_ENTER_SLIDESHOW_GLACIAL 0x09
 #define CMD_ENTER_NORMAL_MODE 0x0F
 #define CMD_ENTER_WAIT_RFWAKE 0x20
+#define CMD_GET_BATTERY_VOLTAGE 0x21
 
 #define WAKEUP_REASON_TIMED 0
 #define WAKEUP_REASON_GPIO 2