I recently replaced the battery and alternator on my '01 XJ. I noticed the voltage was running a tad low so took some measurements with the DVM. With the engine running voltage is 13.6 and battery voltage is 12.8. The new battery has more CCA. Does this sound OK?

Alternator P/N: PURE ENERGY13906N
https://www.rockauto.com/en/moreinfo.php?pk=3371922

 

the alternator won’t charge unless it needs it. mine charged and ran fine @ 13.4-13.8 for years, daily driving. it never did not start, even in sub zero weather.

 

Sounds right to me. The battery voltage is right and the alternator is charging properly.

 

As others said the numbers look fine but it could be misleading regarding the battery as you had the engine running. The best way to check a battery is to fully charge it and let it rest at least a couple of hours, then take a voltage measurement with no current draw (disconnected or no accessory’s, door lights, etc on) The fully charged voltage of a lead acid battery will vary slightly with the design, type of the battery, temperature and its age. The “at rest” voltage at room temperature should be approximately in the range of 12.6 to 12.8 volts. A voltage of 12.25 volts indicates the battery is only about half charged. You can see that a relatively small voltage change indicates a significant difference in battery charge.

 

You could leave your lights on for a while and then start it up. I'm pretty sure you'll see higher voltage output from the alternator.