2006 Mitsubishi Galant car shut off

My car was on and parked (idling). It just turned itself off. It would not turn back on but the lights and odometer were flashing, even after I removed the key. Wierd. Tried a jump, but that did not work and then my husband took a rachet and hit the battery terminals and asked me to try again. Then it started. Now when I stop at a light it does a little shake, like it wants to shut down, but it hasn't again. Yet. Battery test shows a 96% charge (checked at Auto Zone).