Low voltage with new battery even with car started???????

[jdmd16]

Just installed new battery, but the car wouldnt start so i push started it, got a nasty popping sound from motor(not exhaust) but it stopped after about 10-15 sec and ran smooth. i then checked voltage and it read 11.9 with car started. i shut the car off and it wouldnt crank back over unless i push started it. i did change my ground wire to a 9in. braided ground strap which i grounded to the fender and i even tried to ground it to the headlight bolt thinking that it was a bad ground any suggestions appreciated

[Lule]

Check that the plug at the alternator is firmly seated, the belt snug, and that the battery has plenty of water.

If these check out, do the running voltage check again. As a guess, you should have about 13.5 vdc at idle.