Battery draining over night

I continue to lose the battery charge over night. I disconnected the positive and negative terminals and checked the voltage drop across the battery terminal to the cable and noticed about 7V. I then pulled fuses one at a time (inside and outside) with no change. I then replaced the alternator, still no change. Has anyone seen this? Curious as to what would cause the approx 7V drain that is not on a fuse.

You state that you are losing battery charge overnight. What is the reading across the posts when you stop driving it for the night versus the reading in the morning prior to starting the car?

If there is a big difference, you may have something turned on just enough that it is causing the drain without you seeing it.

Years ago, my parents had a car that was having a problem similar to what you are describing. I took a DVM and hooked the leads between the positive battery post and the positive battery cable and set the reading to check for current. Sure enough, there was current drain and I ended up turning every switch and rheostat until I saw a change on my meter. My problem ended up being a light switch that was barely turned on. You couldn't see any light action, but there was enough of a drain to affect the battery.

Good luck!

The battery voltage when it is being charged properly is about 13.5 VDC. After the car is turned off the voltage should be around 12.5 VDC.

I suggest letting the car set for a while with nothing tied to the battery to test if it is draining internally. This isolates the battery from everything else for fault diagnosis. If that looks good, then you connect the battery terminals and remove fuses. The alternator is not fused so it is always in the circuit. Ther may be some other components that are unfused but I am not aware of what thery are. A leaky alternator could drain the battery.Plug one fuse in at a time and check for excess battery drain.

Thanks for both of the helpful posts. I forgot to mention that the battery was replaced first because the old one was cheap and had gotten very low on water, I thought that seemed the logical reason for going bad. I did remove every single fuse one at a time and checked the voltmeter (I could try again with all fuses removed and replace individually).

At this point I have been monitoring the battery voltage while the car is sitting - the battery maintains 13.5V (does that seem higher than normal?) with no drop, even with the 7V load from neg term to ground.

Thanks again

"At this point I have been monitoring the battery voltage while the car is sitting - the battery maintains 13.5V (does that seem higher than normal?) with no drop, even with the 7V load from neg term to ground. "

Ryan, I do not understand what you are saying here about the 7V load. Are these measurements taken with the cables removed from the battery terminals? Are you getting a 7V reading between the battery cathode (neg terminal) and the chassis ground with no cables to the battery?

The 13.5V reading is high for an at-rest battery. Are you measuring that across the battery terminals? What reading do you get when the battery is being charged by the alternator? What is the voltage between the anode and a convenient chassis ground (not the battery cathode) while the car is both running and at-rest?

Warning: Do not run the car while the alternator is disconnected from the battery! You will smoke the alternator!

Tom

I see the 7V load when I disconnect the battery and test from the neg terminal to ground. The 13.5V is from pos terminal to neg terminal (~14.5V when running).

After changing out the alternator, which includes the V regulator, the battery now maintains a fairly constant charge of 13.5V at rest.

I see the 7V load when I disconnect the battery and test from the neg terminal to ground. The 13.5V is from pos terminal to neg terminal (~14.5V when running).

After changing out the alternator, which includes the V regulator, the battery now maintains a fairly constant charge of 13.5V at rest.

I do not understand how you can be measuring such a high voltage across the battery terminals (13.5 V) at rest. I suggest checking your voltmeter on another car battery to make sure it is calibrated properly.

If the running voltage is as high as 14.5 V then that warrants a check of the voltage applied to the field terminal of the alternator to determine the quality of the connection. If the connection is faulty then the voltage seen at the terminal will be lower than the battery voltage. This in turn forces the alternator to put out more current to the battery than necessary, overcharging it. This can cause the acid to boil inside the battery and perhaps come out of the vent ports.

I do not understand how you can be measuring 7 V from the cathode to ground. If the battery is totally disconnected from the car as I infer, then you should be measuring 0 V. A voltage as high as what you measure indicates some kind of leakage path from the batery to the car chassis. Is your battery tray wet with water or acid (see above paragraph)? Do you have a metal hold-down bar across the top of the battery that could be conducting current though acid at the battery top?

When you connect the ground cable back onto the cathode you should measure a voltage between cathode and chassis of 0 V. If not then you have a faulty ground cable or corroded connection between it and the chassis or battery terminal.