Battery Drained

Hi all Newby today, my 3l s type sucks the battery dry if not started for a few days.any clues appreciated.

Hi Shannon,

First thing to establish is whether the current drain is abnormal or if you have a failing battery. If you have a multimeter with the means to measure current, when you have parked up your car, with everything off, disconnect the negative terminal of the battery and connect the multimeter to measure the current. Once all the lights go out you will probably see 500mA or so. This should quite quickly drop down to 300mA and then about 150mA as the modules go to sleep. After 24 hours if all is well the current will be down to around 50 to 55mA. This is normal.

If this is what you find then it’s likely the problem is the battery. If you see a lot more than quiescent current than this it’s time to start isolating the problem by pulling fuses but try the above first.

BTW, what year is your car?

Reminder: Make sure you have the radio code before disconnecting the battery.

Shropshire, UK

Welcome Shannon. Your profile indicates you have a '99 S-Type.
Battery drain - first question is how old is the battery? They don’t last forever.
Is it dirty and corroded? Dirt conducts electricity and corrosion impedes conduction, so be sure your battery is clean.
If not that, then something else is not shutting off, could be a relay.
There was a transit isolation relay in the trunk (UK = boot) that the first dealer should have removed, and tucked the wires for it up away from shorting contact. Is there water in your trunk? These wires have been known to fall down and get in the water and crud that builds up in the trunk.
Here is a link to an old thread on this subject. Click on the title to read it with the responses.

When I attended NP00 (New Product 2000) training class in late 1999 we were advised that the X200 will take 45 minutes to get to a resting state of about 30 to 40 milliamps.

I hated that because it took a LOOOOOONG time to diagnose quiescent drain.

The best way to diagnose is to open ALL the doors and boot lid, then close the door latches (doors open) and place something in the boot lid switch to simulate CLOSED.

Now you can access and measure circuits without ‘waking’ the car. (Opening the doors etc.)

You will disturb the car by turning on circuits or removing certain fuses and then you have to wait the 45 minutes ALL OVER AGAIN!!!

People have reported that the ignition switch (faulty) has been known to cause a battery drain.

Happy diagnosing.


G’day, it’s definitely not the battery as it’s brand new. Do all S types have a twistable knob to disconnect the negative terminal? The previous owner had been disconnecting to stop the problem. Thanks for the advice so far. Luckily it’s not a daily taxi so not an urgent issue.

Just because the battery is new, do not discount it from being at fault.

Bob is correct, after 45 minutes your quiescent drain should be no more than 30mA.

Usual suspects for parasitic drains are;
Chirp sounder battery short circuiting due to age or water ingress.
Ignition barrel flap. Remove the key and the flap should close.
Check the modules in the boot for signs of water ingress.

Good luck.

Thanks will do, flh inner door lock(black locking mechanism above handle) is stuck out, could this be part of problem?

Will search boot for stray wiring. Thanks for tips.

I had the same on one of my doors where the black locking button couldn’t be moved. It was due to the latch mechanism not completing its locking cycle.


I have the door trim off at the moment, what did you do to rectify the problem. I was going to try seperating the cable from latch to test if the latch will lock.

The ignition barrel doesn’t completely close, what does this effect?

For the latch problem, I dismantled the mechanism, replaced a faulty microswitch and re-assembled. Has been good ever since.

For the ignition barrel, give it a small squirt of some lubricant - some say WD40 but it really isn’t meant to be a lubricant. There is a switch in the barrel which senses key in. When in it activates the seat and column memories if you have them and tells the system that a key is present and when out it allows the central locking to work and probably initiates the car going to sleep. This might be your problem.


This sounds very promising I have WD-40 or a silicon lube will give it a try.

When my ignition barrel flap failed to close after removing the key, and I opened the door, the dashboard would chime as if the key was still in. I used Lock-Ease on it.

Cheers mate, this is Jagoogle ,just ask and somebody has an answer. I gave it a drop of silicon lube and jiggled the key in and out a bit, it seems to be closed more. Will listen for the sound next drive.

G’day all , a drop or two of silicon lube on the ignition flap and it seems to have fixed the issue. It has sat for days on end and hasn’t lost power. Thanks for the tips

Glad to hear it and thanks for the update.:slightly_smiling_face:

In my case the problem was the backup alarm chirp sounder.Car is a 2000, 3litre. Access was tight. Disconnect battery and lift engine fuse box and holder out of the way. Looking into where the holder was and towards the front you will see a silver unit with a plug attached. Disconnect the plug and reassemble. Fault is due to a rechargeable battery in this unit failing due to age and the car battery constantly trying to recharge it resulting in a flat battery. In my case I am not worried about the backup alarm so have left it disconnected with no problems. Otherwise use procedure to diagnose if this is unit responsible for flat battery. Apparently you can access the plug from inside the rh wheel well by removing the wheel arch liner, but I can not confirm this