Battery doesn't hold a charge even though battery and alternator are new
 

Hey all, I'm new to this website. I have a 1987 Camry (4 cylinder, 4door). I don't really know much about cars, plus my usual mechanic is stumped, so I thought I'd bring my situation here. My car has 187,000 miles on it. I bought it used at 156,000 miles. Beginning 1 year ago, the car battery started holding less and less of a charge, giving a slow crank at startup. Eventually, the battery would no longer hold a charge from the alternator, and died alltogether. I went and bought a brand new batttery for the car. Within 2 months, the (new) battery was dead, also no longer holding a charge. Took my car to my regular mechanic. First thing he did was start the car, then disconnected 1 of the battery terminals. The engine immediately died. He explained to me that the problem was the alternator. It was no longer working properly, so it no longer giving the battery (or the engine) the juice they needed to stay operational. He said the car needed a new alternator. He put on a brand new alternator, and charged the battery to full capacity. New problem. Even with a brand new alternator and a fully charged battery, if I let the car sit for more than approx. 7 days without using it, the battery completely dies alltogether giving me NO crank at startup, not even an ignition click when I turn the key. Took the car back to the mechanic. He tested the output voltage of the alternator and said it was perfectly in spec for my car. I suggested putting in a stronger powered alternator. He said an alternator with too high a voltage output will overcharge and damage the battery. I have not been back to him since. What I did (for the meantime) is bought a Schumacher portable charger. When the battery's cranks start sounding too slow, I take it out, charge it overnight, and put in back in the car before going to work the next day. I have to do this 2 or 3 times a month.
My question to you all is, what could be making every battery that I put in that car drain within a week of non usage? If the alternator is in spec and works, why is the battery not getting charged sufficiently during normal use? And why would a fully charged car battery DRAIN EMPTY if the car has not been driven for 5 to 7 days? Any help regarding this matter would be GREATLY appreciated!

It sounds like you have an electrical leak somewhere. In other words, you are losing the battery charge while the engine is off. The way to figure out where the charge is being lost is to first hook up a meter to the battery. It will show how much electricity is being used due to the "leak" (a short).. Then pull each fuse one at a time and see which one stops the electrical leak. When you pull a fuse and there is no change in the leak amount, put it back in and then try the next one. Eventually you will find the circuit where the leak is. If finding the circuit shows only a partial improvement that means more than one circuit has an electrical leak. In that case, leave the fuse on the leaking circuit out and continue the process until you find the other circuit where the other leak is. Depending on the circuit with the leak, repairing it could be easy of difficult. I have no advice on that.

If your handy with tools. When not driving the car for a time, disconnect the negative battery terminal to stop any drain. When going for a drive, reconnect the battery. If the battery is still charged there is a drain.

Don't disconnect the battery cables with engine running as this can damage the alternator.