1985 300SD Alternator charging erratic , sometimes 11.4 at startup, usually goes to 13.0-13.3 after about 5 minutes running but sometimes goes that high at startup. After going to 13 it usually stays and vary slightly with load changes. Battery checked good at battery shop, alternator checked good but replaaced it anyway and conditions still seem about same. Car is not used for long runs lately and low battery started me checking system. Is the voltage behavior normal, Mercedes manuals not real clear. Thanks for any comments. Benny