The Battery is just a Storage device for "Stray" Electrons (Humor)
One of the larger drains is the headlights,and if your Alternator were ill
the Headlights "Draw" might lower onboard power enough to affect/effect
all the fancy computerized engine controls.(Low Voltages do funny things)
Since your diagnostics are already 'hollerin about the Headlights I'd start there.
(I know Nothing about Headlights...To me it's a Bulb that's either
Good or Bad)Try the simple Voltage test outlined a couple of lines below.
Worn brushes in the Alternator's Voltage Regulator will cause erratic power.
Of Course there could be something wrong with your Headlight system,causing
it to pull more power than it should.A Bad Ground wire for the Headlights
will play havoc.
First inexpensive test would be to see what the Voltage output of the
Alternator is with the engine running...Multi-Meter leads on the Battery
posts,with engine idling,'Should be between 13 and 14.1 volts.
Then turn the Headlights on and see how much difference in Voltage.
If the Voltage drops below 12 that may be your problem.
There is also something called Amperage,BUT you have to have a DC clamp
meter to test that.
I'd suggest one of the Big auto chain stores...They'll all test your Alternator
output for free...BUT, Too Many Electronic Wonders under your hood for them
to Accidentally fool with.
Inexpensive Multi-Meters to be had at Harbor Freight and Sears
(less than $20.00 on sale)
WAI is a big Wholesale only electric parts distributor to the rebuilding trade.
(BUT you can see parts available for your Alternator)
http://www.wai-wetherill.com/products/sresult1bom.cfm?ManufName=BOSCH&item=0-123-320-046
This is the Voltage Regulator ,with Brushes for your Alternator.
http://www.wai-wetherill.com/products/partimage.cfm?wai_num=IB387-1
"D+" and "FLD" are the Brushes.
They also offer just the brushes:
http://www.wai-wetherill.com/products/partimage.cfm?wai_num=38-91800
#430 in the Cyrillic Pictograms is the Voltage Regulator.