Voltage Drop

[Patcon]

2 minutes ago, Dave WM said:

Check to see if there is a current draw with the key off.

What he said ^^^^

[Zed Head]

3 hours ago, DoubleYOOHZ said:

 What I dont understand is how my battery dropped from 12.4V to 8V from just two days of just sitting the garage. 

When you connect or disconnect the negative cable at the battery do you see any sparks or hear any relays clicking?  You might see the tiniest of sparks from the clock power draw but sizable sparks and/or relays clicking would show that you have something turning on that would drain your battery.

[Dave WM]

or could just be an internal short on the battery. charge it with a charger and leave it disconnected for a few days. If it was mine I would just buy a new quality battery. I will check my current draw to see what it is later, I imagine the clock can't be more than a few milliamps.

[DoubleYOOHZ]

18 hours ago, Dave WM said:

bad battery/ bad cables/bad battery terminals. I would not use a battery that had gone thru a deep discharge cycle for what ever reason. You should get it load tested at least and make sure you have good quality cables/terminals and everything is clean. Check to see if there is a current draw with the key off.

I did have a bad connection with the negative cable. When I got it back from the shop, it was struggling to start. We wiggled the negative cable and it started right up. Seems to be the area where I crimped the wire was getting loose. I will try replacing that negative cable. How would I check to see the current draw with the key off? 

16 hours ago, Zed Head said:

When you connect or disconnect the negative cable at the battery do you see any sparks or hear any relays clicking?  You might see the tiniest of sparks from the clock power draw but sizable sparks and/or relays clicking would show that you have something turning on that would drain your battery.

I have not taken the battery cables off yet. However, when I have there are sparks and relays clicking. 

16 hours ago, Dave WM said:

or could just be an internal short on the battery. charge it with a charger and leave it disconnected for a few days. If it was mine I would just buy a new quality battery. I will check my current draw to see what it is later, I imagine the clock can't be more than a few milliamps.

I had charged it with the charge and it starts up beautifully. 
Do you folks know what is the average voltage reading for an idling car? The fact that my 280z was getting a voltage reading of around 13.XX V was just alarming since it is barely charging. When I gassed the charge, voltage reading never exceeded pass 14 V. 

[Zed Head]

24 minutes ago, DoubleYOOHZ said:

I did have a bad connection with the negative cable. When I got it back from the shop, it was struggling to start. 

I have not taken the battery cables off yet. However, when I have there are sparks and relays clicking. 

The fact that my 280z was getting a voltage reading of around 13.XX V was just alarming since it is barely charging. When I gassed the charge, voltage reading never exceeded pass 14 V. 

If you're sticking your meter probes on the cable ends you'll see what the alternator puts out but it may not be reaching the battery.  So that bad connection needs fixing.  Your voltage numbers look fine, it doesn't seem like you have a charging problem.  The sparks and relays clicking show that you have a wiring problem that is leaving things powered up when the key is off.  That's why your battery dies while sitting.  You need to find that wiring problem.  But the alternator and regulator seem okay.  

Try to figure out which relay is clicking and it will give a clue about the wiring problem.

 

[Dave WM]

My point about the internal short was even if you charged it, that does not mean it will keep the charge even if its completely disconnected.

[Dave WM]

so your are getting sparks and sounds of relays with the KEY OFF when you connect and disconnect? As far as checking for current draw with key off, no point if you are getting sparks and sounds, that needs to stop and then you can look for MINOR current draw.

Edited September 26, 2016 by Dave WM