1998 Mitsubishi Montero XLS electrical issues

Hello Experts,
I am experiencing a mystery I hope you can help me solve.
This is the first time I have experienced any problems with the electrical system. A few days ago, after 1 day of being parked, my car wouldn’t turn over all the way. It was acting like the battery died. We assumed a dome light was left on. A jump start seemed to fix it. I drove to work and back (3miles rt). The next day I went to start it and it was very weak in turning over. I was able to give it gas and get the thing to idle. I drove around doing errands with no problem. After returning from the store, while in the parking lot, the ignition did not engage at all. That is to say there was no power to the dash. There was power to the door light when I opened it, and the reminder “ding, ding” sounded because I had the key in the ignition, yet still now power to any of the dash or console lights. I kept the key in the on switch and put the driver side window down then up (electric). I turned the key and the dash lit up and the engine turned over. Today while my husband used the Montero it was weak in turning over but it did. Then while driving the thing started to cut out on him. He had to pull over, put it in park and give it gas to keep the idle. Then he proceeded to drive on. He checked the battery for water-good. He checked the connections for corrosion- no corrosion. He unhooked the battery and re-hooked it to get it to start the next time. No obvious signs of decaying wires. We think the battery is original. Any help is appreciated.