Originally Posted by JOHNSHENOUDA
I have an 84 vette. new battery, alternator, etc. not had any issues until last week. battery was completely dead. checked to see if something was one. Nothing. Charged up the battery. noticed that i was not getting any sparks on the negative cable so I used the chassis to get the ground. battery charged right up and I was pulling 14 volts. Drove it a couple of days now problem. then let it sit for three days and again battery was dead. Had the same problem with the ground. Charged it a second time and again no problem so far. could the negative cable be causing some sort of drain? what could be killing the battery ?
With everything electrical switched OFF disconnect the battery ground cable and place a volt meter positive lead to the battery side of the cable or post depending on where you made the disconnect. Touch the ground side lead to the chassis where it will make good metal to metal contact. Observe any voltage reading on the meter. If a voltage is present, this tells you that some circuit is sneaking power. The offending circuit can be isolated by pulling the fuses one at a time and observing for the drop in leakage voltage at the meter. The alternator is another source of potential leakage, so you want to disconnect it from the system. Internal failures aside, the diodes tend to drip a little currect all the time so you want this thing disconnected except for testing its contribution (if any).
Batteries are also a source of internal leakage of individual plates to others or cells. About the only way to determine if there is enough internal leakage to cause a discharge is to have a battery tester that can put a heavy load on it while tracking its ability to sustain that load for a prescribed time period. Most decent battery shops have the specs by battery and the equipment to perform this.
Also, a simple at home test of alternator output is to switch everything electrical on with the engine running about 1500 RPMs. Then with a volt meter tapped off the battery's positive terminal test the systems output. The alternator/regulator should be able to hold 13.5 to 16 volts against the full operational system load. If it can't hold 13.5 there will not be enough excess voltage available to recharge the battery. If the output is higher than about 16 volts, with or without the full system electrical load, the battery will be overcharged. This heats up the plates and electrolyte which can result in plate warpage and steaming the electrolyte out of the battery.