Batch Submit SAPUI5 - How to get correct BODY format?

I am trying to get my POST call working using Batch but I am getting an error about my payload. I am new to SAPUI5 and am looking for guidance.

I am getting this error when I make the call from the UI

When I execute the call I am trying to replicate in SAP Gateway Client it looks as so and it works.

Content-Type: multipart/mixed; boundary=changeset

Content-Type: application/http
Content-Transfer-Encoding: binary


SRMShoppingCartItemCollection(NUMBER_INT='0000000001',OBJECT_ID='1004266',DOC_MODE='EDIT',WIID='000000000000')/ItemAccountAssignmentNavigation HTTP/1.1

Content-Type: application/atom+xml
Accept: application/atomsvc+xml;q=0.8, 
application/json;odata=fullmetadata;q=0.7, application/json;q=0.5, */*;q=0.1
DataServiceVersion: 1.0
MaxDataServiceVersion: 3.0
Content-Length: 372

<a:entry xmlns:a="" 
<a:name/></a:author><a:content type="application/xml"><m:properties>

However, When I try to submit through my custom exit in BATCH I am unsure how I am to submit the BODY of the payload?

var sServiceUrlBatch = "/sap/opu/odata/srmnxp/SRMSHOPPING_CART/";
var view = controller.getView();
var assetList = [];
var that = view.getController();
var batchModel = new 
var batchChanges = [];
var json2 = {
          number_int  : "0000000001",
          object_id   : 1004277,            
for ( var k = 0; k < 2; k++ ) {

batchChanges.push(batchModel.createBatchOperation("SRMShoppingCartItemCollectio (NUMBER_INT='0000000001',OBJECT_ID='1004277',DOC_MODE='EDIT',WIID='000000000000')/ItemAccountAssignmentNavigation", "POST", json2) );


How can I put my JSON2 variable in the correct format that the gateway call is looking for?