There are a few things that can cause a car battery to discharge over a short
period of time, but I hear about the diode bridge in the alternators causing
this quite a bit. The Bosch units do this too. If you are handy with a
multimeter, measure the output (V) of the alt to make sure that is in spec,
then measure for ripple current in Milliamps (if I recall correctly). Since a
diode allows current to flow in 1 direction only, it acts like a switch; if it
goes bad, it will allow current to flow in the wrong direction as Rick stated.
A bad diode bridge or 'pac' won't always show up as a charging problem unless
they 'open' instead of 'short'. BMW's run into this- it's funny to hear of a
dealership totally stumped over an 'old' 80's 535i with a slow power drain,
and someone posting on a digest or to a club magazine (Roundel in this case)
gets help with the problem (for free).
Good luck, you will find it! Post the result when you do,
John McDonald
future owner of a certain 72 BRG TR6 if there is a God...
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