Hi Paolo,
Refer the link below
http://help.sap.com/saphelp_nw70/helpdata/en/3f/8deebc8d714bb6a7ba8c40997526f1/content.htm
Additional information
To load banalce your background jobs you need to use Tcode SM61 --> Job-Servergruppen --> create the group and assign your servers. The same group then you can assign to each batch jobs.
Hope this helps.
Regards,
Deepak Kori