So I was gone out of town for 9 days. Jag wouldn't start. Battery was at 11.78 volts. Charged it up. Started the car fine as usual. Monday, it was 12.4 volts once charged. Today, it is at 12.1 volts. I have no clue as to why it is losing charge. I have been working out of my house lately, so drives are short when I do go somewhere. Battery tested fine.

Also, is my alternator bad or going bad? On a cold start, no accessories, voltage is 14.1 from the Battery. Once warm with literally all exterior lights on, and radio playing loud, it reads at 13.5 volts.

2002 xj sport

 

You state she sat for 9 days, ....how many days did she sit for the other 2 measurements? Check you cables for corrosion, ....even if you see a little, almost assuredly there is a lot down into the cable and it will need replacement. If I am not driving my car for more than a week I slap the battery tender on it. Check your grounds for corrosion, there are several. Check for swelling of the battery case, any swelling pretty much guarantees a bad cell, even though it tested good. Its very similar to a 4 pack of say AA batteries in a device, if one of the batteries is bad, it will cause the others to die quicker.
Check the connections on the alternator and if possible, get it tested, it could be a bad voltage regulator.

 

Your alternator is very good. The loss of battery charge is either because it is on the way out or because it is being drained by something in the car electrics. Check the battery drain first - disconnect the negative battery cable and insert a multimeter, set at 10A range, between the battery negative post and the disconnected negative cable to monitor the battery drain. To do this correctly, you will need extension wires from the battery and to the back seat, the thickness of the wires to be such that you can close the boot lid and the rear door over the wires then connect the multimeter and place it on the back seat so that you can see the reading through the window. This is necessary so that you can take the ampere readings without unlocking the car and opening the boot or any door. At the moment of connection, the multimeter will briefly read a few amperes which will soon drop to below 1 A and continue dropping over time. See what is the final ampere reading after at least 1 hour when the car electronic systems shut down process is completed. If the reading is more than 0.03 A, you have a current drain somewhere.

 

Awesome! Sounds very doable! Once the rain calmed down, I'll get to it.

 

You have all the symptoms of a failing battery. How old is it? Should be a sticker on it for age.

 

January 2015. Rain all day today, so couldn't do a thing. But will report back as soon as the rain stops.

 

So I took the car to a shop because my battery keeps testing good. Prior to taking the car, I told them I believe the car has parasitic draw.

Shop told me "battery is marginal and something was staying on."

Battery still drains in the car. It's weird. If I get a voltage reading with positive and negative cables connected, the voltage reads 12.05

Disconnect them both, and it reads 12.25

 

There is always a draw, but how soon did you do that test for the last time? Upon initial shutdown you will have multiple items in these cars staying on for up to 20 minutes. Cooling fans, radio amp fan, ECU and the items its controlling and then shutting them down. Then the constants...ECU, radio memory, remote receiver etc... When you shut it down, open the trunk (leave it open) and let it sit for about 20-30 minutes to shut down then go out and measure the battery. Don't prompt anything with the fob or open any doors, that will engage the parlor lights and create more of a draw (thus leaving the trunk open). Then after measuring that, open a door to engage the parlor lights and do another measurement.

 

Sounds good will do. Both battery cables are corrosion free.

 

An other trick (which worked best for me) is to open all 4 doors and the trunk, then push the lock pin in each lock.
That lets the car think they are all closed, after which you can use the FOB to central "lock" them.

If you connect the multi-meter to measure Amps. you will see them going down in steps once you central lock, following the different circuits going to sleep.
After some 20-30 minutes, you should get a reading of ~30 mAmp, which is the base draw in full sleep.

Now, when that value is higher, the open doors and trunk allow you to pull each fuse at a time, while watching the multi-meter (or have someone watching it for you).
Once you see a big drop on pulling one, you know you probably have the culprit, then check the according circuit to remedy.

NOTE: I taped each lock to remind me they were locked, just to prevent them from slamming them close during a brain fart ....

 

How old is the battery ? CCA rating? An old battery will drop charge just sitting -- they charging and not connecting and see what happens. My Jaguars can and do sit for months and fire right up.

I would just replace the battery -- my go to has been the Bosch rebranded sold at Pep Boys. They are always having a sale and they have a 3y replace w/o prorate

 

The shop told me they found a 40mAmp draw. But seems like I'll do your method myself.

 

So yesterday, I got the battery charged the local auto parts store. It was at 12.44v when I put the battery in the trunk at 1:30pm. I didn't connect the battery cables to the battery. Just let the battery sit in the trunk. Been driving my other car mean while. Read the voltage just now. It was 12.37v. So that is a day of sitting, and it lost .07 voltage. That makes me think the car does have parasitic draw? I know I still have to perform the test as yeldo mentioned. Which I will.

What I found intereting was this. Battery was wet just now. Even on the negative and positive terminals. I was uploading pics through my phone to post. But it doesn't upload them for whatever reason.

 

Are you getting a weird smell from the battery? Now when you say wet, are you speaking of beading and is it in a specific area like on top and the terminals or all over? That battery should be around 13.2 or so from a fresh charge...it really sounds like its on the way out and really not good enough for these cars to operate with.

 

No weird smell from what I remember. But will check that in the morning. Oh, battery is dated December 2015. Yes, it was beads. Pretty much all over the battery.

 

How can you think about a parasitic draw if the cables are not even connected ...

As indicated, a freshly recharged battery should read a wayyy higher voltage, and keep it there.
I bet on a bad battery ... been there ... mine start to throw incidental messages at anything around 12.4V before starting.
And it takes quit a bit of a drive before it does not happen any more.

 

A good battery will read about 13.2 volts immediately after disconnected from the charger but it will very soon drop to about 12.6 to 12.7 and should stay there if not connected. The reading of 12.4 and dropping in one day shows that your battery has some internal fault and cannot take the full charge but only some 70-80 % (see the chart below). And with it getting wet, I would immediately replace it.

 

I was typing faster than my brain was thinking at point I said parasitic draw because, it still managed to drain a little with the cables not connected. Brain farts lol.

 

Performed a parasitic draw test. I had the Red on DC 10A, and the Black on the COM. Knob on meter on the DC 10A. Black probe was pointed at the negative battery post, and the red probe was pointed at the negative battery cable. It started at 3.0 amps, and kept on jumping from there. But it settled it at .46 amps.

Everytime I pointed the red probe to the negative battery cable, I would hear the CD player come on. It was very evident. But when it stopped making noises, it settled at .46 amps.

This was with leaving the trunk open for 30 minutes. And then i performed the test.

 

0.46mAmp is a bit higher than the Jaguar value of 30mAmp, but a general rule is that everything under 50 is good to go for modern cars.

I am also not sure if with the trunk open, but not locked, every system is sleeping after 1/2 hour, after all you got some lights and related systems linked to the trunk (like the valet parking).
You should be able to check there by pulling the fuses.

But quick conclusion is that your car is fine, and that the battery is on its way out.