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Originally Posted by socalsharky
Can you be more specific? What did I do that could kill the battery and the alternator? I realize that complete discharges are hard on the battery, but what should I have done differently?
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Yes I can. The alternator is designed to come on and off. In the off mode, it essentially freewheels and stays nice and cool because it's not generating any heat to produce electric current. If you look carefully at the alternator, you'll see it has it's own fan built-in to provide cooling, keeping the bearings and the circuitry (diode pac) nice and cool. Believe it or not, these things can produce a lot of heat. So much so, that there are currently several cars on the market which use water-cooled alternators.
If the battery is significantly drained, even though it's not discharged, it makes the alternator work longer just to replace the current in the battery. Add to this that even a partially drained battery can upset it's internal chemistry so much that sulphate crystals (from the electrolyte) can form on the lead plates. This lessens the amount of surface area for the necessary reaction to take place. So, in addition to being low on current, it now has a lessened ability to 'make' that current, meaning the alternator has to work even longer. Then, with a weakened battery, it's ability to absorb electrical fluctuations (or act as a buffer) is also reduced, placing the diode pac in the alternator under greater stress, making them die prematurely.
One problem many people have is that they view the battery and alternator as separate components instead of equal and mutually dependent partners in the charging system. Most people believe that a bad alternator killed their battery, when more often, it's the exact opposite - a bad (or less than optimal) battery is what killed the alternator.
I know it will seem like overkill to many people, but if leaving the car for more than even 48 Hrs., the battery should be either disconnected (which people are reticent to do for fear of losing the radio pre-sets and DME adaptive memory) or plugged into a maintainer, which many feel is cumbersome. This is why the type which plugs into the lighter socket is a good idea, it's convenient.
After 48hrs. the battery is still usually capable of starting the car and this is most people's gauge of their battery's health. But they are ignorant of what it may be doing to the alternator over time by making it work 'longer'. And even their car's range (MPG) can suffer, because an alternator when 'energized' (working) has a parasitic draw of between 3 and 8 HP crank HP which could have been used to drive the rear wheels. So, the shorter the alternator's operating time, the more fuel can be used to actually propel the car. This may only result in 5-10 more miles/ tankful, but it is measurable.
Cheers!