Obtain a VOM(voltage ohm meter). Set it on the DC 20 scale. Place red lead on battery + post; place black lead on battery - post.

Fully charged battery reads at least 12.60 volts. Less than 12.60v does not means battery is shot, it just means it's not fully charged.

As Sixto pointed out, your battery may be gone. This test will tell the tale.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"