240z battery drain

You have a parasitic draw on battery

How to identify and locate a parasitic drain - YouTube

It sounds like the alarm system is on or that you have a relay that is stuck.

1. Press the Unlock on the remote key fob to make sure the alarm system is turned off. Sometimes when the battery has gone dead, it doesn't reset properly, just try again with the battery charged and installed.

2. If that doesn't work, you may have a relay that is stuck in the ON position. You have a fuse/relay chart both in the passenger compartment and engine compartment and can pull the specific fuses/relay for the emergency flashers to verify if that it is the problem. There should be a chart indicating the location of that specific relay and the fuse.

hi Larue.
You're late for work and rush out to your car, only to find that it won't start. The headlights are dim and the engine simply refuses to turn over. You realize that your battery is dead. But how did this happen? There are five main causes of car battery drain or failure.

Human error

You've probably done this at least once in your life - you come home from work, tired and not really thinking, and left the headlights on or didn't completely close the trunk. Overnight the battery drains, and in the morning your car won't start. Many new cars alert you if you've left your lights on, but may not have alerts for other components.

Parasitic drain

Parasitic drain is due to components in your vehicle continuing to run after the key is turned off. Some parasitic drain is normal - your battery delivers enough energy to keep things, like your clock, radio presets, and security alarm operational at all times. However, if there's an electrical problem, parasitic drain can exceed what's normal and deplete the battery.

Bad charging

If your charging system isn't working properly, your car battery can drain even while you're driving. Many cars power their lights, radio, and other systems from the alternator, which can make the battery drain worse if there's a charging problem. Then you'll be stranded at roadside with a stalled car that needs a boost. And even then, bad charging will drain your car's battery. A professional mechanic will be able to diagnose what's causing a charging problem.

Defective alternator diode

A car alternator recharges the battery and powers certain electrical systems. If your alternator has a bad diode, your battery can drain. The bad diode can cause the circuit to charge even when the engine is shut off, and you end up in the morning with a car that won't start.

Old battery

If your battery is old, it might not hold a full charge. If your car consistently won't start, it's possible that the battery is worn out. You should generally replace your car battery every 4-5 years. If your car isn't starting consistently, and your battery is old, battery replacement should be the first thing you consider.
Having a battery that won't hold a charge is frustrating, and figuring out what's causing the problem can be tricky. Assuming that the cause of the battery drain is not human error, you will need the assistance of a qualified mechanic who can diagnose your car's electrical problemsand determine if it is the battery or something else in the electrical system.
you can read up some more at this link.

What is the most battery draining part when car sits over night Google...

use a diagnostics . it tells you everything even reset your cars computer

First are you sure the alternator is charging the battery ?
If it is, someone will need to pull fuses and disconnect major circuits until you find the drain. It could be a simple relay, or a short to ground in the harness somewhere.

I think I would attack the drain problem first. Something has to be draining the battery, it does not have to be a steady drain. It could be something serious for 30 min in the middle of the night. You may need to pull fuses one at a time to try to narrow down the circuit. it could even be a weak component in the alternator or computer. I know you said you replaced the alternator.
If it goes down overnight, it should also go down during the day. Can you leave the meter connected and check it every hour or so ? ?
Another component that could be suspect is the key switch. I know you said you checked it, but it could be a part-time problem.
When the starter or relay clicks, I would want to know how much voltage I have at the starter post, and coming out of the key switch. Then how much at each point in between. You also have a neutral safety switch in that circuit.

If it's clicking, it's not a fuse , its a Relay. Relays Do sometimes stick. Or it can be clicking due to low voltage that was caused by something else.

To see if that's your issue, charge the battery, take the Relay out of the car and see if the battery stays charged after 12 hours.
If teh battery stays.. then first step is to replace the relay.

To hyjacker Jeeda
and others.

Yes, all cars can do this, we call it KEY OFF phantom drain.

most cars spec list ILLEGALL drains (spec)_ as over 0.050 amperes. (50mA max)KeyOFF.

Here is a short to do list to find it. (most steps need ammeter to find it, )
1 A dark garage. find lamps stuck on, every INCH of car inside and out. go slow and look (bingo?)
2: connect the ammeter to the battery PLUS lug. see that drain? illegall? now, key off for sure.
3: now unplug every fuse 1 by 1 to find the feed that has drain. (cab/ eng.bay) unplug and put back. actions.
4: unplug all relays, same way as fuse, found it, yet? see drain go away is he goal, simple goal.
5: ok 3 or 4 finds bad feed line with drain,we then unplug all things 1 by 1 on that failing feed found above.
6: ok nothing found yet,(cause) move ammeter to huge wire on the Alternator, lub, see a drain there (BINGO bad ALT)
the below ammeter (amp/clamp) is the most easy way to find Phantom Drains. bar none

unless the scan tool scans told you what was bad ?
a Phantom drain allowed to persist can wreck the battery in just 24hours.
THE METER must DO DC amps (many do not and costs tad more for DC amps) DC CURRENT
AND A 2AMP RANGE. at least.



https://www.amazon.com/Current-Auto-Ranging-Digital-Ammeter-V-Alert/dp/B094R8CB4W/ref=sr_1_10?keywords=dc%2Bamp%2Bmeter&qid=1659787362&sr=8-10&th=1

on my meter it has autozero button that must be pushed 1 time in current mode. to calibrate it first ,and clamp; the wire first. (better meters cost more)
I put a STAR icon to show the amp lamp test points, (battery cable and ALT) simple example.

The best way to check for a power drain or a "draw" on the battery is to dis-connect the negative, or "Neg" (-) side battery cable and then connect a test light not a meter, between the "Neg" (-) side battery post and the battery terminal at the end of the battery cable.

With the key removed, all of the doors closed, and no accessories turned on, and also if there is a light under the hood dis-connect it for now. Normally the test light when connected should start off bright and then quickly dim down until the test light is almost not even showing a connection and the filament inside of bulb that is inside of the test light will barely glow and not even light up, this is normal and the only thing that should be drawing power is the KAM (Keep Alive Memory) for any control moudules or accessories that require a KAM. If this is the case then the condition of the battery would be suspected of being at fault and an internal short inside of the battery will not show up as a draw on the battery, and the battery voltage will slowly drop off all by itself with nothing even connected to the battery.

If the test light does not dim down and stays bright, or it will dim down but will also still dully light up the test light, then there is a draw on the battery and if you start removing the fuses until the test light dims down and barely makes the test light filament glow, then you will know what circuit is at fault, but if the light never dims down with all of the fuses removed, the doors are all closed, and no accessories are turned on, then dis-connect the wiring to the alternator and if the test light dims down to almost nothing, then the draw is in the alternator itself.

Common places to find a draw are the vanity lights inside of the sun visors are not turning off or are shorted, the power door lock(s) are faulty, or after-market accessories that are not properly installed, and there is even the possibility that something metal has dropped down into a cigarette lighter or a power point and is making a connection there, such as a watch battery. Also check the wiring for any wires that have been melted together or if they are missing insulation allowing the wires to touch each other or a body ground.

Front seating area, passenger side, under dash, mounted on support bracket under glove compartment not all fuses will light tester unless the its on