My new patch? Yes, I did successfully make a battle background hack that is slightly better than Driver's because I found a better way to change backgrounds. It is still based on his code, but with the help of Jambo and Darth, I branched his code so that a var is loaded instead of a random byte.
Feel free to grab it and test it out on DrFuji's vms. I haven't expanded the bg table yet, but I have been able to switch the backgrounds by setting var 0x40F7 to the bg number. The bg table is at 0xF10000 with the first 23 entries filled. I have no idea what entries 15-23 are and they don't work as backgrounds, but they are still a part of the table. I think they have something to do with a battle having the same background but different palettes, but I'm not sure.
Either way, take a look!