In the Owner's Manual (page 11-5) it is recommended at 100,000 miles (under normal driving conditions). So you are only about 10% overdue.
It is recommended to be changed at 50,000 miles if the vehicle is used in severe conditions (page 11-4);
vehicles mainly driven in heavy city traffic in hot weather, in hilly
or mountainous terrain, when frequently ...
One of two things happened:
While you were attaching the jumpers to the Legacy, you dislodged the connection and caused it to go black.
You attached one side or the other backwards on the initial attempt, causing a short, rather than a jumper circuit.
I'd suggest your issue was actually #2. Since there was a lot less juice in the Legacy battery than what ...
Sorry for the long response in advance. Transmission fluid changes are a hotly debated subject so there's a lot of information out there. This is my attempt to try to boil it down so you can make an informed decision.
I've been researching something similar recently and here were the understandings I gathered. Based on what you said, though, (and the ...