1998 Mercury Sable battery drain

I had a 1998, Mercury Sable 6 cyl overhead valve, with around 107,000 miles. I had to keep replacing the battery, alternator, four times, and the starter twice. Finally, I took it to the Ford dealership after having it to a local mechanic who could not find the problem and had checked all the fuses. Well, it was a fuse, the one outside the fuse-box, and the battery terminals had to be replaced as they were not tight enough on the battery. That's it. Prior to that, earlier in the year it needed a transmission replacement and springs. After the fuse problem solved the constant battery drain problem, the O2 sensors went, and the dealership said the car was not safe as the rocker panels were rusting. I did love that car though. One other problem I remember many years ago having was the coolant reservoir would heat up underneath and the coolant would drain out, so I had to replace the reservoir two or three times. The car was sitting at a place for repair, and the guy mowing the lawn saw the coolant leak under the car, so they took out the reservoir to find it had a leak underneath where you might not think to look. The next time that happened, I knew to tell the repair shop to look underneath the reservoir. I also had a diverter valve cause the service engine light to go on. At the time, many years ago, it cost me a lot to fix that, mostly because of the diagnosis time. I had to spray inside the door hinge at times, or the inside light wanted to stay on. The window panel buttons in the door had to be replaced or the window would not go up. There was corrosion they said, and maybe a fuse too. The heater did not work well at all, and I never had it fixed as they would have had to rip out the dash board to get up under for the heater core. The air worked fine always. Other than those problems, I loved driving this car. It was a comfortable car with a smooth ride and some oomph. I miss the comfort. Safety is a comfort currently in a newer car.