Well we used to use it as a daily commuting car, about 30 miles round trip per day, but we’ve since begun using our more gas efficient vehicle and carpooling, so this is now maybe a 2 - 3 times per week short trip vehicle. Short trips being roughly 30 miles around, to the grocery store, errand running, etc.
Someone else will give you a more definitive answer on this, but I think you’d be better off replacing the entire alternator, especially if this is a junk yard alternator. Get a new/rebuilt one with a warranty. If I recall correctly, trying to replace just the regulator requires some work, and doesn’t guarantee anything.
{I think it’s not a drain but actually insufficient replenishment by the alternator. }
I’m inclined to agree.
somewhat off base, where is the battery located in this car, I don’t know. However I remember SAAB in one model, used to locate the batt right nest to the exhaust, so it go tnice and hot, too hot unless you had all the heat shields in place.
Thus I’m wondering if you may have a heat shielding or cooling problem, which is drying out your batts. dry bats do not work very well.
that aside, buy yourself a DVM and check the voltage after a spirited 30 min trip and while still ideling, it shoudl be ~14V. If you wished to monitor the battery, you could make yourself a little monitor using a LM3914 IC and some diodes and just watch the voltage as you drive (and hopefully charge the batt).
Yeah, but a new alternator is $300, plus labor, which I’m not really willing to pay. This car has EVERYTHING wrong with it. I know, it’s less than car payments, but this car has been so unreliable, which is troublesome when you have a three year-old kid and need to get places. 
OK, when you do use it, you’re running the engine long enough that the charge used to start the car should have been replaced by the alternator, assuming everything is working correctly. I was concerned that you were only doing a couple of 2 mile hops (for example) and that might not be sufficient time for the charge to be fully restored. If your visual inspection does not turn up any defects, the next step is to get someone knowledgeable and with the right tools to check the charging system.
The dimming lights may also just be due to the extra load the window motor put on the system. If the lights went really dim then a intermittent charging problem may be occurring. Regardless, you stated that there is a current drain in your original post so I assume that the battery dies when the car is parked for awhile so that is a different problem.
If having to spend a few hundred dollars perhaps to fix this problem is on the border line then you may as well cut your losses now. There will most likely be other issues later on.
Very good point. If you’re not willing to pay $300 (or around that) to get this car running properly, then dump it and buy something else. If you can’t afford something else…well…you either pay to fix this one or you gotta walk. An old Volvo 740 probably wasn’t the best buy for someone on a tight budget, I would’ve gone with a slightly newer, cheap Cavalier.
A new battery going dead while sitting idle is the sign of a voltage draw; failure to start or dying on the road is another problem altogether.
It has been mentioned by your mechanic that the method of pulling fuses while using a test light or VOM to determine if there actually is a draw is a valid one and is easy to determine. If there is a draw then finding that draw may be easy or difficult, with the most difficult problems being related to anything involving dome lights, door switches, cigarette lighters, etc.
My opinion at this point is that you should dump the car immediately. You’ve thrown batteries at the car by the case, have no idea what the problem is, and repeatedly state that you do not want to pay someone to find the problem nor do you want to spend money on a new alternator if needed. It’s time to throw in the towel and move on. Buy a ho-hum old generic Chevy or Buick and skip the Volvo profiling.
(There’s also a misinterpretation of the regulator business; the regulator does not have carbon brushes but the alternator itself does.)
There is a simple, methodical procedure when cars have an electrical problem and this should be performed every time there is a suspected battery, starter, alternator, or volt. draw problem. Check it all at once and weed out any and all potential problem areas at once.
JMHO anyway.
“(There’s also a misinterpretation of the regulator business; the regulator does not have carbon brushes but the alternator itself does.)”
I assume it has an alternator with an internal voltage regulator where the brushes are attached to the regulator. If it’s like mine, the regulator/brush assembly is cheap (about $40) and very easy to replace.
NEW DEVELOPMENT! I just threw the new battery in, tightened the connections, and NOTHING HAPPENED. Last time, the lights and the dash would come on, but no starting. This time, no lights, no dash, no noise, no nothing.
Is this it? Is this the end?
This is starting to sound like a loose connection someplace, maybe the ground connection from the battery or the grand strap from the engine. This “new development” should make it easier to diagnose.
This just means you’ve been looking in the wrong place for a long time. You probably have a bad connection or bad relay somewhere and you’ve replaced a few good batteries. But, as others have said, if you won’t take it to someone who knows how to diagnose the real problem you should just sell it and forget it.
You know that guy down the street who works on cars? Yeah, that one. Tell him you need his help.
In additioin to the loose connections, look for the possibility of the cable being internally corroded, if the main cables have a “U”, moisture coudl collect inside the insulation at the bottom of the “U” and simply corrode away the wires.
Examine all your grounding straps also.
With the new development you should consider the possibility that the electrical part of the ignition switch is faulty. (not the key and tumbler)
One small thing you want to make sure of: when you turn off the ignition (key) make sure the switch is turned all the way to the OFF/LOCK position.