Alternator guage is oscilation light is blinking

Unfortunately I don't have the money to fix my power-steering unit for I have been without a job for several years and am in very bad health with no money coming in. I'm concerned in that I have to travel a 120 mile round trip to my doctor and I'm afraid that the alternator/battery is not reliable enough to make the trip. I can afford a fifty dollar alternator from the junkyard, as my rebuilt alternator only lasted about seven k miles so why shouldn't I get one from a junkyard? The reliability couldn't be much worse, the alternator that was on my car originally lasted 110K.
My (personal mechanic, in whom I completely trust, who has worked on cars his entire life, and my vehicles for 35yrs, his father was Bobby Allison's mechanic who was burned badly at the race track) said that the alternator is charging, I took it to him to let him check it out, he said he'd put a another on one at no charge because the rebuilt one on there now has only about five to six thousand miles on it. But because I seldom drive the warranty is out of date. He said it was charging at 14v and when the gauge dipped down to just above the red zone it was still charging at 9v. Immediately going back up to 14v.
When the rpm is around one k and I quickly give it gas the alternator gauge needle will go up but then go down to just about the red zone for a moment then go back up to around thirteen. I drove it yesterday and the needle, while it usually stays at thirteen went up to 15 just below the red zone and stayed there a for about fifteen minutes before dropping back down to 13, it's normal charging number. Is this because I had left my negative battery cable hooked up over night and it had been drawn down because of the parasitic electrical draw? Or because the battery is down to it's last three quarter's of life, this battery is only about two years old and is the top of the line O'reilly battery. I have have had to charge the battery about six times because of the parasitic draw killing my battery when I forget to unhook the neg. Bat. Cable. I only drive to my Dr.'S office, grocery store an pharmacy so I don't get to charge the battery every day. Should I hook up a trickle charger? I have to buy prescriptions every month and have to watch every penny, or just unhook the neg. Bat. Cable as I only have a couple of hundred dollars and don't know where any money will come from after that is gone. I just can't keep replacing eighty dollar battery's every eighteen months.
I took the battery to O'Reilly's cause my car wouldn't crank and they said it was completely dead, they charged it and checked it and said that it had about thirty-five percent of life left. Once charged it started right up which was a blessing cause I thought it might be the starter. Later on I took the negative battery cable off and checked the volts and after about fourteen hours of siting in the garage I checked it again and the voltage seemed to be the same.
If I had a new battery and the alternator went out how many miles would my car travel if I turned off all electrical draw from the battery?
I just checked my bat. 9-27-15 /with my multimeter after sitting all night and most of yesterday afternoon, and the V reading was12.13 and the parasitic draw was 0.17. I have all electrical systems including my air shocks suspension system unhooked. Is this simply the computer draw? Is my best course of action to unhook the neg. Bat. Cable when I finish driving it?
"replace belt and tensioner as recommended is 60,000 mi. " This was done less than ten thousand miles ago when the Alternator was changed because the belt came off.
Your advice is greatly appreciated, God bless you.
Jack Andrews

Thank you for your quick reply.
Will the powersteering fluid if it gets inside the alternator have a detrimental affect on the alternator itself?

I took my car to my mechanic day before yesterday and I'm having the powersteering pump replaced. It wasn't as expensive, the pump that is, as I though it would be. The labor on the other hand may be a killer because it was at the very bottom of the motor. I don't know why but It's one thing after another wilt this car. I like the car, Buick park ave ultra supercharger, but it just seems that I can't get five k miles on it without have something break. It only has 110k. And was owned by my uncle, mom, and myself so it has been well taken care of. It has been garage keep yet all the paint has peeled off. Cheap American garbage. It will be the last American vehicle I ever own. They all get their cheap parts from the same companies.
Jack Andrews

My brother has had two pathfinders and has had very little trouble out of either of them, they have over 250k and other than routine maintenance only had transmission replaced.