Q: Total electric failure - 2003 Plymouth Aztec

My daughter has a 2003 Plymouth Aztec. About two weeks ago it began sputtering and shutting down at stop lights. She could get it started again, but with much effort. Each time this occurred, there would be a "funny smell." That problem seemed to rectify itself, but last week she drove home from the store, and turned off the engine. 15 minutes later her husband went out to use the car, and all the electrical began flashing; then nothing. The key fob will not work. The Aztec is completely dead. She did tell me that they had to "jimmy rig" a used battery to get it to fit a while ago. She said they tested the battery, and everything else electric, but can find nothing wrong. After reading your article on battery cables, I wonder if, when they were "jimmy rigging" they could have damaged a part of the cables somehow. What is your opinion on this problem? Thank you. Elaine
My car has an automatic transmission.