Can I set the Contact Batch Payment Details?

The Xero API allows you to download the Batch Payments for a Contact but these are 'read only' - you cannot currently upload these via the Xero API. You can set and upload the Bank account number of contact.

Only users with the bank account admin permission can view and update contacts bank account details via the Xero web interface and unfortunately at this time the Xero API does not support granular permissions to allow updating bank account details via the API. You can vote for this feature on the Xero Uservoice site here.