Ok guys I have a 2012 xjl and I get this message battery low start engine every day ,had the battery checked and was told good battery had voltage checked on alternator and put out 14.1-14.4 volts ,I can drive car around all day it will start fine but if I lock doors and it sit overnight it will not start completely dead battery , what could it be ,maybe something draining battery,it just started this this weekend. Your suggestions would be greatly appreciated.

 

I did notice the button for the flasher still illuminated when locked what is the cause or that

 

Dontay, the button for the flasher will remain lit. It will go out after about 20 minutes. From the sounds of things, you may have a stuck relay. That or a cell that is going dead. Granted, how did they test the battery. Just a voltage check or did they do a load check. If they did a load check, what percent capacity did the battery have. We have found that if the battery starts getting below 75% capacity, you start having random issues.

What I would say to do is to simply drive your car and get the battery up to 100%. Before shutting off the car, open the trunk and connect a multimeter across the battery. It should read 13.7 VDC if it is down around say 12.7-12.9 VDC, then we have a charging system problem. Now, shut off the car. The battery should quickly fall to around 12.7 VDC and then finally to 12.6 VDC. If you are down around 12.5 or 12.4 VDC, we either have a load on the battery or a cell that is going south on you. From here, you will need to create some jumper leads (does not need to be a heavy gauge wire, 22 gauge wire is more than adequate. But, connect the wire to the 2 battery terminals and run them outside the trunk and close the trunk and lock the car. Connect the multimeter to the 2 wires. Did the battery voltage go up to 12.6 VDC. If yes, then this pretty much will confirm a bad battery. If the voltage is down around 12.5 VDC (ie, has about a 10 amp draw on the battery), then we have something that is remaining on in the car. You can then leave the car sit over night and measure the voltage in the morning. If you are down around 10.5 VDC, then this confirms a bad cell in the battery.

Lets do these initial checks and see what we have. Too many possibilities to be really replacing parts at will.

 

Yes I had the battery load tested but I am gonna try ur method tomorrow thanks

 

Load testing is worthless. You need a new battery. How old is the one you've got? Typical life is about 5 years.

 

I agree with Mark SF. Change the battery first and see what happens.
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Although it is likely the battery, I agree with Thermo. There are some quick checks that don't cost anything, require nothing more than a multimeter, and can confirm it isn't something other than the battery. I prefer to verify before spending the money. Especially if the verification is cheap and easy.

 

While I agree with the above, I think the OP needs to be realistic, and understands the battery, if it's the OE one, is now 8 years old, and they don't last forever. I replaced the battery in our 2016, this past September, simply because it's four years old.....

 

After two different Jag dealers and a new battery I figured it out via the forum. I installed Allstate milewise device in ODB port. That causes the battery to dissipate - overnight several days if fully charged. Solution is to leave device in, close door and do not open, disconnect negative connection in trunk and wait 30 seconds. Re-attach and after 15-20 minutes the red lighted triangle on panel will be out. If it is not, you are draining battery. Supposedly there is a software fix so I don't have to deal with negative connection (make sure tight). Anyone know?