Severed 10 gauge wire from positive jump start terminal

Car wouldn't start. Charged battery, still wouldn't start. Wiggled wires off the battery connections. Discovered that a 10 gauge wire, connected via crimp-on ring connector, that slips over the "jump start battery post, " was severed. Found the other end of it and it looks to go through the firewall under the dash to either the Fuse box or the BCM (I think. I'm not a mechanic.). My first thought was to butt splice the wire with a good quality, heat shrink butt splice. But by the time I cut back enough wire on each side of the destruction caused either by rodent damage or rubbing against the hole in the firewall. Manufacturer didn't see fit to put a grommet there. I don't see teeth marks on the wire, just a lengthwise slice and fraying of the aluminum wire. I may not have enough wire left after cutting back to good wire, to complete the repair. I would like to replace the whole run of wire with a new piece of stranded copper which I have in appropriate length and gauge, but as I can't see where it connects, I don't know what connector I'll need to put on it. I also don't know if I'm physically able to get to the location it needs to connect to. (Old lady, bad back with many surgeries under my belt.) I also know it's not a good idea to splice copper to aluminum. What all is required to access the space this wire is supposed to connect to? And what kind of connector goes on the BCM or fuse box end? Car is listed above convertible touring edition and I can't drive it to a shop as it sits. Also right before I had the no start condition, it threw a C Can Bus error. Something about a fuel sensor.