Seems that you definitely have a problem with current drain while engine is off.
A quick test with a voltmeter will verify it's charging OK when running.

In fact if you can drive more than 20-30 minutes without needing a jump then I'd say it's charging OK - because driving without charging would drain the battery and the engine would quit without battery power to support it.

Our '90 came to us with the fuse for power door locks and dome light disabled. When I replaced the fuse I got a persistent dinging from the chime. I never took the time to trace down the problem. Probably a bare wire inside the driver's door switch (near hinge, the one that turns the light on/off), or just maybe a power lock switch that's always "on". But the removed fuse was the quick fix for a constant battery drain.

Try that and see if it helps.

--
DAMHIK: Don't Ask Me How I Know - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 500 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).