: Inaccurate Battery Voltage Display??

07-18-06, 12:51 PM
Here's the situation.. I almost always drive around with the coolant display on but I decided to switch it to Battery Volts when I have my subs going. When driving on the highway I noticed it was reading around 12.8 to 13.4.. thought the 12.8 was a little low but didnt get too worried. However, i'm driving in the city (nyc) in traffic with my A/C on and my sound system off, and see my voltages steadily dropping allllll the way down to 11.8. So at this point I get very worried and shut my A/C off and I see it start to climb to 12.4 fast, as soon as the light changes, I give it a little gas and it keeps moving up to 12.8-13.1.

So today I take it to get my electrical system checked and the guys comes over afterwards telling me everything checked perfectly fine and why was I concerned. I explained the A/C making the voltage drop and he brings me over, I turn the AC on to replicate the conditions and sure enough my voltage display reads 11.8. Then he brings me over to look at his tester which is reading about 13.3 -13.4

Here are the exact test results he gave me :
Battery Volts - 12.78
Batter Amps - 650
Charging system volts - 14.78

Battery is a 2 year old Optima Yellow Top
I have new tensioner,idler, drive belt ETC.
So what could possibly be going on? :confused:

07-18-06, 08:59 PM
Where did he check the voltage while the AC was on and the dash gauge showed it as being low? He probably checked at the battery, right?

I suspect that the voltage drop under load occurs somewhere else. It could be a bad ground or bad positve side connection or fusible link. You would need to start taking readings at the battery and go back towards the dash.