So yesterday I took my mini out to the lake and on the drive there the car drove perfectly normal without any issues. Then comes night and people begin to leave the parking lots.

I turn on my car, starts perfectly fine. Lights turn on and everything works. 2 minutes later the DSC and traction lights come on when idling. When i revved the car a bit more, the lights turned off.

Buddy told me to try turning the car off and back on again. Did that, the car didn't start. Hear some clicking noises as if the battery died. Luckily I was still in the parking lot and was able to push my car back into a parking spot.

So we jumpstart the car, everything turns on. But when I switched on the headlights and start turning the wheel and I notice that it became difficult to turn, as if the power steering was going out and at the same time headlights start flickering as well. Turn off the car and back on, battery is dead again.
We jumpstart the car again and this time we make sure to leave the headlights off so that it could give a sufficient charge.

So we wait for the car to charge a bit and then the car suddenly began overheating. I check inside and notice the overheating gauge light is lit up red, but the needle is sitting at the very bottom as if nothing is turned on. Gas gauge was doing the same thing as well.

We let the car cool off a bit and jumpstart it again only this time, none of my gauges worked. The rpms and speedometer were both frozen. None of my gauges worked. I tried rolling my windows back up, those didn't work either. Powersteering was also gone at this point. So basically the battery is completely dead at this point, but the car is still running.

Since it was 4th of July, all the stores around us were closed so the only choice we had to get back home was to drive the mini without any working gauges, dead speedometer/rpms, no powersteering, no headlights at 11pm in heavy traffic. Scariest moment of my life. Luckily we had 2 other cars with us and they sandwiched me in between so I could use their lights. In order to make sure that my car doesn't stall in the stop and go traffic, I had to keep the rpms at around 1800 (don't know exactly since cluster was dead).

We drive about 45 miles in 40 degree weather with both windows down and heater at full blast and then we decided to pull over to let the traffic behind us get by. An idea comes to us to just switch the batteries with one of our other drivers Camry. We do that, and bam. The car works perfect. All the lights are on, windows are finally rolled up, its as if nothing was wrong with the car to begin with. We put the dead battery into the Camry and try to start it up and thing happens. Jump start it and it starts working. Since the Camry has less electrical components, it was able to get enough juice to drive back home without any issues.

So we swap back our batteries to see if that helps with anything and mini was able to start up just fine with the old battery!

Comes the morning, I go to Autozone to see if the issue was with my battery and was told that it's healthy, holding out 12.4v. I'm guessing it's because the Camry was able to charge it up sufficiently. But then how was I able to drive on the Camry's battery all the way back home(another 80 miles)? And why wasn't my alternator giving my original battery any juice?

 

Seems like the alternator on the MINI is kaput. Battery ran down and you started getting electrical gremlins. Most cars can run 30-90 minutes off the charge in the battery. So Camry battery was charged and that restarted the clock. Your battery was ok and the Camry charged it for you.

You need to get your alternator tested.

 

Wow! What the hell could that be? Mini sounds like it's posses.

 

Crank -damper failure....
It let go...
So the load from the alternator makes it spin...so no alternator....thus the PS pump shuts off...and the sc is not getting spun at speed, so the waterpump, which works off the sc is not running...so the car overheats....
Then the computer is seeing the wrong amount of airflow with the sc not running right, and the ecu tosses codes....
So you tossed in a battery at 100% charge...so the Alternator did not put a big load on the damper...so it gripped....
But I would say it will likely happen again.....
Inspect the crank damper....
Jack the car up....take off the passangerside tire...then pull back the liner....if the damper shows cracking it tearing it's done....if it flexes lots, it's done....

Now a weak alternator might explain everything too....if you don't have much power, and the ELECTRIC COOLING fan cannot run...and stuff starts to fail...
But guess you need too look.....and check the voltage at idle and under full load, at idle, and slightly higher idle....but honestly, still look at the crank damper....so many fail, it is a matter of when not if.

 

Ditto, crank damper failure.

 

I disagree about the crank damper. It wouldn't go away when the fully charged battery was swapped in the way the OP described.

Doesn't hurt to inspect it of course.

 

Alternator is dead simple to test and very likely. Eliminate it early.

 

I would think the same thing except the tester they use at AutoZone tests everything, charge / regulator /output /load.

Also, when checking the damper also check it's pulley alignment, because it's the rubber between the damper and pulley that fails, in rare cases it has been known to fuse itself back together temporarily.

 

So i took my new Walmart battery into autozone today and it tested at 12.2. When i revved the car, it jumped to 12.8. Autozones tester couldnt test the alternator because the voltage was so low. Could it be the alternator now? Or some wiring issues?

I also found this user who had the same problem back in 2010 but he has yet to respond. https://www.northamericanmotoring.co...lternator.html

 

Might be....that's at about the lower limit...but the amps it can output here is important....
Lower output voltage like that is a sign of wear...and a battery in that car will never get a full "float " charge at 14.5 volts or so to prevent sulfation.....
Since you yanked the alternator off...did the crank pulley look ok?
Edit...saw you tested it on the car....
Usually the battery must be 100% to test the alternator...so running for about 15 minutes after a start.....
Testing it right after a start , especially if the battery is not charged doesn't tell you much....could be a bad battery cell at that voltage...

 

Alternator should be putting out 13.5 to 14.1 or so with the engine running even with a bad battery. Think your measurement still points to a bad alternator. While it's not much fun, you can take it off and carry it into an auto parts store to test on the bench before spending any money on it. Or take your buddies fully charged battery with you and do the on-car test with the fully charged battery.