Unless you left the lights/stereo on and drained the battery why not replace it? Running around with a bad battery is the quickest way I know of to cook the diode pack in the alternator.

This would also be a good time to clean all the battery corrosion underneath the battery tray. Don't be surprised to find the corrosion has eaten through the inner fender wall. Pretty common problem with the W126's. Relatively easy fix using some fiberglass mesh and an application of POR-15 or similar product.