Re: My battery died on the water
Charging system check:
Check your battery voltage before starting the engine. It should be around 12 volts. Then start your engine (jump start if necessary) and check the voltage again. With the engine running you should get between 13.5 and 14.5 volts. If the voltage is lower than 13.5, or higher than 14.5 you have a charging issue. Too low and the battery won't charge. Too high and you cook your battery.
Shut the engine down and wait a few minutes. Now check your battery voltage again. If it dropped back down below 12 volts, you probably have a dead cell, or excessive current drain.
Cranking check:
Next, do a voltage check while having somebody crank the engine. Put your meter leads directly on the battery posts, not on the cable clamps. While cranking, the voltage should remain above 9 volts or so. If it drops below this, your battery is most likely bad. If it does not, proceed to the next step.
Connection check:
Now check again while cranking but this time, put your positive lead on the batteries positive cable clamp, and the negative lead on a bare metal piece on your engine block.
You should get the same readings you did while directly on the battery posts. If you get a lower reading, you have a poor contact/corrosion somewhere in your battery cables.
Test for current drain:
If all these steps pass, disconnect your positive battery cable and set your meter to read amperage. Turn off, but do not disconnect, all electrical equipment. Place the positive meter lead on the battery post, and the negative lead on the battery cable. If you get a reading higher than a few milliamps, something is draining your battery. Disconnect things one at a time until the current draw goes away.
NOTE: ideally, with everything turned off, you get zero current flow but many modern electronic units, most notably CD player/radios have some parasitic draw that maintains programming memory, time etc. These values should be very low, less than 5 milliamps. This draw will eventually drain your battery in time, but it would be over a period of several months.
Edit: Yuppers... rectifiers are notoriously fickle about polarity. If reversed, they carry the batteries full current capacity straight to ground and go "POOF!" This also makes the charging voltage test a bit iffy. With an open rectifier, the voltage drops. With a shorted rectifier, it may not drop, but it becomes an AC voltage which will not charge a battery.
