Lots of panel lights then nothing

Something was humming when I left this morning. Did okay there. About halfway home, I noticed the battery light on, and at the light it hesitated accelerating. The lights started coming on one by one. I turned off everything extra I could turn off. The radio, air, even my windshield wipers. It was raining. Then the lights stopped one by one and the dash panel went black. It was barely limping along. Would only accelerate to about twenty five mph. That is a guess since no panel. Finally got in the driveway. It would not shift into park. Shut off. Was then able to shift into park and I put on e-brake. Next day I went out to look and the panel came on and it acted like it might start, but would not turn over due to not enough power. My husband thinks it might be that the serpentine belt tension-er has gone bad. Any thoughts? I hate to replace the wrong part. I just replaces the battery about a month ago. Menke's Auto Repair had also told me I might have an electrical short. I had not had a chance to take it to an electrical place before this happened.