Went to the garage this morning and found both headlights on. Tried to lock the car with the key fob and passenger side lamp goes on while driver side stays on. Car completely non-responsive, and there is no reading on the voltage meter I have in the cigarette lighter. Eventually, driver side headlamp goes off. I hook up the CTEK, and it's been at Step 2 for about an hour now. At some point during that time the tail lights have come on and are staying on. In this situation, should I disconnect the battery from the car while I have it hooked up to the CTEK, i.e. if the tail lights stay on, is it going to keep the battery from charging?

 

Yes, the car's electronics are 'confused' due to the low battery condition. Honestly I'd pull the battery, get it charged out of the car and go get it load tested. What you've just subjected it to is one of the worst thing you can do to a battery and will damage it's resiliency over time.

In all honesty you should drive the car more often or just disconnect the battery if you are going to leave it sit more than a week. The car is always 'pinging' looking for the key fob.

 

You will only see a voltage on the cigarette lighter when the car is on or for a minute after a door has been opened or closed. If the battery is low it will probably not turn it on with the door opening.

While I don't know about the CTEK, most smart chargers need to see more than ~ 9V or so on the battery terminals before they will start charging. If the battery is below that the charger won't do anything. If it is not charging you need to connect another battery in parallel or a 12V power supply to get the charger to start charging. Or use an old fashion "stupid" charger.

 

The thing is the car is driven pretty frequently with not a lot of short hops less than several miles. This is an AGM battery that I bought earlier this year, and I last drove the car 3 days ago with the voltage meter reading 12.4. The battery should definitely still be under warranty, but I just can't think of what would've drained it so suddenly.

 

I don't know how much truth there is in it. It, I have been advised the drain on the battery is large, short trips of several miles is not enough to charge the battery up and over time will lower the power output until the computers start running the intelligent degradation Sub routines designed to shut of systems and attempt to leave enough power to turn over the engine.
I have been advised that when I leave the car do not leave lights in auto, wipers in auto and turn of the climate control, as all of these left on can increase the drain on the standby systems.
Since replacing the battery hookin in a ctek mxs 5.0 I've had no problems and this includes the convertible roof which is a huge drain on the battery.
As I said I'm no electrical expert, just what I've been told.

 

I'm still confused as to why the headlights were on. It's logical if they were on then the battery would be dead. Sounds like something else is going on.

 

Typically 12.7v is a fully charged battery and 13.5-14.7v is a good running voltage. I haven't measured the Jag so I'm not sure the above is relevant for these however if your battery is dying then it's either not charging fully of getting drained quicker than it should while idle.

If you suspect the battery, again the troubleshooting step is to pull the battery and charge it. Then let it sit a couple days disconnected and off charge and see what the voltage drops to. An internally shorted cell will show up under this test.

On the car you'd need to monitor voltage and ground drops between the battery and the charging circuit. There's a whole list of dumb things that will cause charging problems than simply changing the alternator.

 

When my battery died everything tried to work, from headlamps to windshield wipers. Really a shocking experience to a new owner. Real 'Oh Sh.t' moment.

 

Things just started to turn on by themselves?

 

Lights and wipers may have been set to auto when car last turned off and the low battery charge does weird things over the canbus system.

 

When my original battery died it was right after I installed the Jag Wrangler and was playing with it a lot. I have to admit I've been remotely putting the top up and down a lot again the last couple of weeks without the engine on. Don't know if this by itself could be the cause for the battery draining prematurely, but I'm sure it's not helping.

 

Do it 3 or 4 times with an unhealthy battery and you won't start the car

 

OK now I understand the reason for the drain.
I went out this afternoon to clean the inside of mine. Started it up and put the top down. Shut it down and plugged in the Ctek. Opened the doors and cleaned the interior and leather. Took about an hour. Unplugged the Ctek and started it up and put the top up. Ran it for a few minutes and shut it off. Hooked up the Ctek and cleaned the garage.

 

I have and you are correct.

 

I think it is 2.1 volts per cell and each battery has 6 cells. 12.6 volts is normal fully charged battery at rest. As for charging rates there are 2 different systems used. The 2006-2009 (4.2) cars alternators run at 13.5 -14.2 volts where the 2010-2015 (5.0) cars alternators run a various voltages between 12.6 to 14.5 depending on requirements of the battery module and the ECM. Just my observations.

 

The Ctek device, is this something that is plugged into household current or is it a self contained unit?

 

One of these.

 

The CTEK battery maintainer is powered by household AC. If you park on the street and don't have access to AC power, Amazon sells solar powered trickle chargers with solar panels mounted inside the vehicle. But they don't work anywhere near as well as a CTEK.

 

Simon, did you leave the headlights turned on, or did they turn on by themselves?

 

Each operation of the remote top consumes LESS THAN 1/3 of 1% of a healthy battery's charge.