Rep Power: 0

Can there be damage to Alternator after leaving lights on?

I took my 05 civic to the dealer to have the charging system tested. It tested normal: 485 CCA on stock battery, 12.72V Battery voltage and 14.40V for charging system.

THEN... they left the lights on and had to jump my car when i came to pick it up. They did another test to make sure there was no damage, but came up with these results:

423 CCA
12.50 V Battery
13.48 V Charging system <--- this they say is low

The manager says it could be due to my stereo system (which was OFF the whole time). But then why did it test normal to begin with? So is this guy lying through his teeth?

In case you're wondering here's the wattage:

Alpine CDA-9856 head unit
Alpine MRP-F250 40W X 4 RMS
Alpine MRP-M450 400W X 1 RMS (only pushing a 300W sub)

Experienced mechanics and MECP's please help!

 
Rep Power: 0

Leaving the lights on will not damage your alternator. The alternators purpose is to maintain the battery and all loads while the vehicle is running. If the engine is off the lights are going to be pulling directly from the battery.

Your charging system's second reading is a little low, but it should charge your battery fine.

 
Rep Power: 292

no, what likely happened is that when they left the lights on, they damaged the capacity of the battery. could be that the battery can't reach full capacity now.

 
Rep Power: 264

Hook the battery up to a trickle charger for a while.

Then take some voltage measurements. First thing you'll want to do is start the car and turn it off, let it sit for 20 seconds to clear the surface charge and then take your first battery reading. Then start the car and take a reading at the battery and one at the alternator as well. Then report back to us!

But it sounds like they just drained the batt down so when the alt is charging it's working harder, hence the lower voltage with engine running after the lights were left on. If after the battery gets a good charge those numbers go up again towards the first set of readings you'll probably be ok.