Update API reference link in BatteryService.md

Update link.

Author: Amanda Butler

docs/reference/api/connectivity/bluetooth/BatteryService.md

@@ -8,7 +8,7 @@ The BatteryService class implements the Bluetooth Battery Service as defined by
 
 ### BatteryService class reference
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.6/mbed-os-api-doxy/class_battery_service.html)
+[![View code](https://www.mbed.com/embed/?type=library)](https://os-doc-builder.test.mbed.com/docs/v5.7/mbed-os-api-doxy/class_battery_service.html)
 
 ### BatteryService example