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Re: Vent in Battery

   >car you draw down the battery. So your alternator then tries to charge
   >the battery back up. The alternators put out say 25 to 30 amps right after
   >starting but this only lasts for maybe 4 or 5 minutes at the most. When

   How is this time period decided ? By the volts in the battery ?

You expended "x" energy (watts = volts * amps), and you need to pump
that much (plus overhead...) back into the battery. Takes however long
it takes (depends on how much "surplus" amperage the alternator can
deliver after driving all the normal electrical load, will take longer
at idle (low power generation), with lights and A/C on, etc.).

   What starts/stops the alternator high current production ?

The alternator (in conjunction with the voltage regulator) attempts to
act as a constant-voltage source, nominally holding 14 volts. It will
attempt to pump however many amps it takes (and can generate, via
sucking power from the engine) to hold the voltage at 14 volts. A
discharged battery will absorb many many amps; a fully-charged battery
will accept virtually no amps. In general, "starting" currents
(cranking the engine) is measured in centa-(hundreds) amps, and
"charging" currents in deca-(tens) amps, so rule of thumb is it will
take ten times longer to recharge the battery as it did to start the
car, plus or minus a factor of ten or so . . . depending on the phase
of the moon among other factors.

   >exposion could result. I have seen this happen in a 911 which was being
   >charged at a high rate for a hour or so. Someone then removed the
   >charger without turning the charger off. A spark resulted and BOOM
   >battery acid everywhere.

   My 5000 has a layer of battery-related-white-powder under the battery.
   Does this indicate that the car had a bad alternator ? (overcharge ?)

?Under? the battery? Sounds like a leaky battery! I'd carefully "wash"
it all away! (use baking soda and water to neutralize the acidic mess,
will "bubble merrily away" until no more acid left), flush with *lots* of
nice fresh clean water! Of course this is an under-the-seat battery-well,
right? Ha! Have fun!

   Is there anywhere a Battery/Alternator FAQ ?

   (Whose 5000 just got the second free battery from Western Auto (warranty).
   The Die Hard died hard in a month or so. This one has an 80 month warranty.
   If it goes wrong I am in for some digging ...)

Generally, batteries are a very simple and well-understood design, and
do not fail short of serious manufactoring defect (or improper storage!),
so if a second battery fails soon, you [probably] have another problem,
like overcharging (alternator voltage should not ever go much over 14
volts, else you not only fry your battery, you start burning out head-
lights, engine computers, and the like...). 'Twould not, however, be un-
heard of to have a complany/store ruin an entire inventory of batteries
by improperly storing them...