I'm not sure if where you plug in AC the adapter on a MS905 Mini is the same size set up as a DS708, or if the MS 905 AC adapter even has a 12V output, but if the output is 12V, a portable external12V lithium battery velcro fastened to back of it possibly would give you a lot longer run time.
http://pro.auteltech.com/autelsupport/Diagnostic%20System/18144.jhtml?logoTypeId=95&typeName=MaxiDas