Chrysler Repair: 01 PT Cruiser: hard start when headlights usd

Question
QUESTION: I had the alternator replaced in my car a few days ago. Now when I am driving and have my headlights turned on the car won't start right after. If I let it sit for a while it will start up. It's a bit of a hard start but I was told that's because of the engine having to be replaced and everything in it being rebuilt. I'm not sure if it could be the starter but it seems odd that while driving and having the headlights on that would drain anything.  Thank you for your help.

ANSWER: Hi Justin,
Your PT only has a warning light for the charging system rather than a gauge that shows the voltage. But first verify that the charge warning light is working by noticing when you turn the key to the 'run' position before you start it does the warning light come "on" which it should do. Then when you start it notice if the light goes totally black. It you have access to a voltmeter check to see if the reading across the battery terminals is about 14.6V when the engine is running and the headlights are "on". If all that checks out then consider the age of your battery compared to its warranty as that could also be marginal.
If that too checks out then you may have a warm engine hard start problem. Use the ignition key to try to find a fault code: turn it "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window to see the mileage reading replaced by a 4-digit number preceded by a P. Let me know the number and we'll go from there.
Please read the PS (below) and respond to it.
Thanks,
Roland

---------- FOLLOW-UP ----------

QUESTION: The light does come on then go away. I did the "on-off" trick and it was P 1684.

Answer
Hi Justin,
The 1684 is simply reporting that the battery was disconnected recently, which of course happened when the alternator was changed. The charging light is working. So, aside reading the voltage when operating and considering the battery life remaining I don't see a reason why it should be harder to start hot when you have been using the headlights as compared to when you haven't been using them.
Thanks for the rating, kind remarks, and nomination. Please feel free to do the rating and nomination again if you choose.
Roland