Do not rely on resistance checks to verify the integrity of high-current circuits. Typical resolution of a typical ohmmeter is, at best, a few tenths of an ohm. Pull 50 amps through a mere 1/100th of an ohm and you've got a half a volt of drop drop across what your meter showed to be "good".

Start the engine, turn on every heavy electrical load (high beams, blower on high, etc) and measure the voltage difference between the battery negative post (not the cable connection at this time) and the alternator case. A "good" ground would be expected to drop less than a 1/10th of a volt. Repeat for the battery positive post and the alternator B+ terminal.

"Typical" battery voltage in a perfectly functioning system could be anywhere between 13 and 15 volts. The actual voltage will vary based on battery state of charge, temperature, load on the system, and other such variables.