The battery died. I tried to jump it but this time when I turn the key all the way, all the test lighting lights up, but I only hear a faint click. Any ideas what's wrong? AAA says the battery is good.

 

Sounds like they are wrong. What voltage does it have? You want about 12.8

 

He mentioned it was saying 12.9. Yet I can't jump it even if I keep the cables connected for 10 minutes. I felt the AA guy was being dishonest somehow even though he didn't even have a battery that fits.

 

Charge that poor battery!!!

A jumpstart is something you do in an emergency to get the engine started and make it home. Now that you are home, put away the jumper cables and troubleshoot properly. Step #1 for any electrical problem is to charge the battery. Step #2 is go online and buy an angry venomous cobra. Keep the cobra with your jumper cables so you are not tempted to use them except in a real emergency.

For that poor battery, You'll want an automatic charger with at least a ten amp output. Don't waste your time with a trickle charger, it won't cut it. If you don't have a proper charger, take the battery to any parts store. They will test it for free and charge if needed, which it probably will.

Do not put much stock in the AAA diagnosis of your battery. Nor should you rely on a simple voltage reading of a battery at rest. Have it tested and charged, and go from there. A healthy battery with an adequate charge should easily power the starter.

P!ease let us know what you find.

 

I was considering this one. It tests, conditions, and charges up to 25 amps. https://smile.amazon.com/Battery-Cha...1&sr=8-10&th=1

 

Also keep in mind a battery gradually loses the ability to store as much as it did even the week before & eventually you have to replace it. A load test should reveal it if done right.

 

As suggested a good battery is important, but there could be other possibilities. Check all connections including earths are clean and tight.

If battery is charged and showing enough voltage, check the small wire going to the starter motor. With the key in the cranking position it should read 12v. With ignition on but not in cranking position is should read zero volts.

If you are not getting 12v when cranking, then you may have an immobiliser fault. If you are getting 12v only when cranking, and your big cable connection is good, then you have a starter motor fault. Before writing the starter off, check you have precise battery voltage at the big wire.
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P. S. I would think most AAA guys have the equipment and should know how to tell if you have a faulty battery.

 

Yep, that should be fine.

Was AAA able to get the engine started with a jump? Or did you have to tow the car home?

Had the engine been starting okay and this is a new problem out of the blue? Daily driver? Garage queen just coming out of storage for the winter? Some background history will help determine your next steps.

After charging the battery, hook up your voltmeter to the battery terminals. (Note I haven't asked about the voltage at rest...) Have a helper turn the key to start while you watch the voltage displayed. With a good battery, the voltage should stay above 10.0 under the massive load of the starter. If the voltage drops below that point with a fully charged battery, you've got two possible scenarios:

1) The battery is on its last legs, and can't supply the massive rush of electrons needed to spin the starter.

2) The starter is defective and is drawing more current than the battery is designed to supply.

The first option (tired battery) is WAY more likely than a bad starter. If unsure, take the battery to a store and have it load tested. You're actually doing a simple load test of the battery by reading the voltage with the starter engaged, but the amp draw of the starter is a variable that could skew the results. In rare cases, you could condemn a good battery. With a dedicated load tester, the load is fixed so the results are more accurate.

Remember, it's normal for battery voltage to drop with the starter engaged. If the battery voltage doesn't drop, or only slightly so, there is a problem in the command side of the starter circuit. Open the hood and find the source of the "faint click" you heard. Was it relay R20 in the front power distribution box? Hold your finger on that relay while a helper turns the key to start. You should feel it click. If so, the command signal is present and the relay is responding properly to this input. If you get the click, try swapping with a known-good relay of the same size from another position. If your wipers work properly, relay R6 (wiper high/low) would be a good donor.

Much of this is a moot point. I highly suspect all will be good with a healthy charged battery. If the battery itself was bad, the fix is easy. If the battery was healthy but run down, you will need to figure out how it got that way, such as a marginal charging system or something discharging the battery overnight.

 

This is how it originally happened. I started the car, went to the car wash. Started again. Went home and then it didn't start. I jumped it and I ran it for about two hours. I immediately tried to restart, and it never started again since. It was also completely drained by the morning. Called AAA. They were useless.

 

If I don't start the car every few weeks the battery goes dead. It's been that way for years. The dealer said it was normal.

 

It's not normal and you have a drain. I had a 2005 S-Type and could leave it for weeks with no problem starting. It is common to have these drains and your talking to the expert on that and it's Karl!
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Perfect, exactly as we agreed. $100, right? I'll get that to you right away.

 

My friend's 2019 Flying Spur has to stay on a charger or it dies in a few days. Again, the dealer says it's normal. They hate that car now. How can you hate a W12?

 

Dealers often want easy money without hassle.

 

How old is your battery? If more than 7 or 8 years old, I wouldn't even mess with it and would get a new one. With age, even the best battery is less able to hold a charge.

You may also have more than one fault in play. Even if the battery itself is fine, it may not be getting a proper recharge due to a driving pattern of inactivity with only occasional short trips with high electrical loads.

You will also want to check your charging system. Measure voltage right at the battery terminals. On a 2003+ model, you should see around 14.5V right after start, slowly tapering down around 13.5V after several minutes.

The last piece of the puzzle may be a drain running the battery down when parked. Details here:

https://www.jaguarforums.com/forum/s...-drain-123535/

 

Yes it's a shame that dealers do that. But I have chased current drains and it is NOT a straight forward or easy thing! With all the modern car stuff about going to sleep and waking up with certain modules it's a complicated mess!

I have spent days waiting for the car to go to sleep only to start checking something and accidentally somehow woke the damn car back up!! Now I get to wait all over again.
Takes a LOT of hours.

Well I thought we had agreed on a higher amount but??
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Now I don't like to post this but with a car that just won't keep from killing the battery no matter what you have done. I have wired a switched relay right after the positive terminal on the battery. I wire that so that the relay closes when I turn the ignition switch on. Then the battery is disconnected when ever the key is turned off.

BUT this creates other problems because without the car being live electrically you don't have an alarm system active anymore. Also resets things like the window memory, radio stations, clock and stuff like that. Plus when the power is restored the alarm goes off. So you need to hit the button on the FOB to shut it off. You also need to manually open the car door because no power until you turn the key.

It's a pain but if the car is draining the battery so bad that you can't drive it then do what it takes.
Of course just a manual battery cutoff switch can work to and it's dead simple to install.
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