electrical question - '77 spider

[Christopher Keen <ckeen@domain.elided>]

Hi All,
Lately I've been having problems where the car just seems to completely lose
power (electrical, that is), always signalled by a loss in brightness of the
headlights, among other things. I took the battery out, charged it, and let
it sit for a week, and it  held a constant 13 volts. Now I've put the
battery back in the car and let that sit for a week. The voltage went down
to 12.6 and then to 12.5, but hasn't decreased any further. Is this an
indication of some sort of current drain somewhere in the circuit? Or is it
normal? The only thing that could have used electricity in the last week is
the interior light when I opened the door. 
As far as I can tell, if this is normal, the only two things remaining in
that circuit for me to test are the regulator and the alternator. Is that
right? When I've tested the battery with the car running, it's shown a
constant 14 volts coming into the battery. 
Thanks in advance for any advice. 
Chris Keen
'77 spider
Los Altos, CA

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