i bought a 30A 450V Littlefuse, 0HEV030.ZXISO, from Mouser, but i think digikey and other electronics vendors could also supply them. i have a 20 AWG jumper that i made and am considering to replace the fuse with that after the OBC warranty expires.
Take a look at the 2013 Ion not charging thread (Active Topics) for some fairly recent repairs and discussion.viewtopic.php?f=23&t=4377
If the MCU fuse opens while charging then it is interrupting up to about 10 Amps of current flowing in a couple of large inductors in the OBC. This produces a large voltage spike as the magnetic field collapses, and the current is looking for a path and it will make a path; if you cannot afford a path, one will be created for you.