You might be able to pull your fuses, and use a multimeter to see if there is any current draw between both sides of the fuse holder aka phantom draw. Check between each set of holders to pinpoint what is sucking down the battery juice.

There's a common reason for battery drain (overnight) in your 1989 240. I'd guess 80% of the time it is caused by crumbled insulation on the wiring to the key and/or lock knob switch inside the drivers door for central locking. Another 19% due to a worn-out delay switch for the courtesy lamp.

If you can do without the clock, courtesy lamps, central locking, under hood lamp, trunk lamp, glove box lamp for some time, take fuse 8 out of your fuse panel to see if the trouble goes away. This is the only substitute for troubleshooting it with an ammeter as Micheal Yount suggests, which can be tricky for the first-time ammeter user. Even so, you still might need to do that if jumping on the common reasons doesn't cut it.

I'm not sure it is related to the running problems, though, but again, I believe every 30-year old Volvo should have a voltmeter in the dash. If not the Volvo gauge, at least one to plug in the cigar lighter jack. They're dirt cheap. It is better than guessing whether the alternator is working based on its age.

--
Art Benstein near Baltimore

Sally, having swallowed cheese,
Directs down holes the scented breeze,
Enticing thus with baited breath
Nice mice to an untimely death. -- Geoffrey Taylor from Cruel Clever Cat /WC Fields inspired

You're gonna need to get a ammeter on it to measure the drain -- and then start pulling/replacing fuses one by one til you ID the circuit where the draw is. Once you get the electrical system squared away -- then you go back and begin to tackle the drivability problems. Right now, you're just guessing and replacing parts -- sometimes we get lucky in that process, but it's no substitute for actually diagnosing what the problem(s) is (are).