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@Circumnavigator and @bocatrip , to provide information for comparison, I measured my battery's voltage just now after sitting about 3 hours; it was 12.77 volts. I normally keep it on a CTEK maintainer while in the garage, but today left it off after running some errands to give you a comparative data point. The battery was still connected to the car and voltage was measured at the CTEK quick connect after disconnecting it. This effectively read the voltage at the car's jumping posts. Note that if your CTEK is permanently attached to your jumping posts, you must disconnect its quick connect to measure voltage at the jumping posts.
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Thanks all for the info and docs, which I’ve saved in my repairs/manuals folder.
So continuing the experiment and saga, I left the Ctek connected overnight on charge instead of condition.
After about 10 hours, I opened the boot and tested the voltage with the Ctek on. 12.75v as to be expected.
Then I disconnected the Ctek and waited a few minutes. Measured voltage again. 12.71v.
Keep in mind I’m doing this across the connections in the boot.
So now, I wait. Will measure every hour or two for another 3 hours until the wife and I leave for the pub for cocktail hour and some college football.
I will measure again when I get home, while monitoring the voltage as I drive each way via OBD.
Then again in the morning, you get the point.
To help explain my obsession with these things, I was a nuclear engineer in the Navy and college was nuclear physics. (Technically P-Chem, but same same) with a focus on data, which is what I do now but in Marketing.
Therefore more data points over time with a controlled environment provides more accurate analysis and experience.
If I connected to car it will not tell u anything. There r a zillion items drawing juice from our cars. Pull it or disconnect everything and try again. You’ll probably just need a new battery with all your efforts. Our cars draw major current. Disconnect and recheck.
Keeping it simple. Recall, P=I*E, the E is your voltage reading. The I is x% (based on read voltage) of the current rating of the battery.
So roughly,
If you read 12.6 v, P= 12.6 v * 900 A = 11.3 kW
If you read 12.4v, P= 12.4 * .75 * 900 = 8.3 kW. For modern electrically managed cars, this is inadequate if the demand was scoped for the number above.
@Circumnavigator , to provide another data point for your comparison, following my 12.77v reading after 3 hours, my car remained overnight off CTEK for an additional 15 hours (at 18 hours total off time) and it now reads 12.73v. FYI, my battery is an Everlast AGM (11/24 manufacture date) per the picture posted previously.
@Circumnavigator , to provide another data point for your comparison, following my 12.77v reading after 3 hours, my car remained overnight off CTEK for an additional 15 hours (at 18 hours total off time) and it now reads 12.73v. FYI, my battery is an Everlast AGM (11/24 manufacture date) per the picture posted previously.
Thanks!
Keep in mind: I am 100% aware that I will be replacing the battery. Just gathering data for fun between now and then.
Im still puzzled as to how voltage went up overnight.
get home after a short drive: 12.43
Next mid morning: 12.57
Going to chalk it up to a bad reading last night and treat the 12.43 as an outlier.
I am planning to both do the half-way up top thing as @Bill400 suggested, just to look around.
Then to crawl my big *** into the boot with the top up and remove the battery area cover, remove the positive and measure voltage at the battery, while disconnected, as also suggested and to familiarize myself with what’s back there.
So, couple quick newbie questions.
1) Anything I need to worry about in doing the top half up thing? Besides supporting the top and tonneau cover? Assuming I’ll have the wife push the button, ask her to stop half way, and I’ll put supports in place.
2) How long-ish do I have after disconnecting the battery before I have to do anything like the reset procedure?
Please consider reaching out to a moderator (Don B) to re-title your post to something searchable for future users with battery issues. You have a bad battery btw:-)
Place my kitchen cutting board on the GB and position it adjacent to the battery
Lift the battery @ ½ inch vertical and pull it toward the cutting board
Walk it onto the CB
remove the vent tube
Slide everything back to the truck opening
Remove the battery without breaking my back
Jump the + and - battery cables for @ 10~ minutes
Charge new battery
Remove the battery cable jumper
Reverse order with new battery
Reset windows
I’m not a slow typist and it probably took as long to compose and type this as it would to remove the battery.
WJ
Ps….a slightly discharged battery may seem to recover a little overnight due to a brief "ionic rest period" that allows chemical reactions to even out, but this does not provide a real charge.
Pps…My XK Service Manual states that the battery must be at 12.5 (not .6) minimum to expect accurate testing results
Place my kitchen cutting board on the GB and position it adjacent to the battery
Lift the battery @ ½ inch vertical and pull it toward the cutting board
Walk it onto the CB
remove the vent tube
Slide everything back to the truck opening
Remove the battery without breaking my back
Jump the + and - battery cables for @ 10~ minutes
Charge new battery
Remove the battery cable jumper
Reverse order with new battery
Reset windows
I’m not a slow typist and it probably took as long to compose and type this as it would to remove the battery.
WJ
Ps….a slightly discharged battery may seem to recover a little overnight due to a brief "ionic rest period" that allows chemical reactions to even out, but this does not provide a real charge.
Pps…My XK Service Manual states that the battery must be at 12.5 (not .6) minimum to expect accurate testing results
Thanks WJ!
May I use a piece of cardboard and a nice thick camping tarp I can slide backwards in lieu of a cutting board?
Went out to start playing around.
As shown above, I tested voltage at the Ctek connector and still at 12.57v as it was at 10:30am.
But alas the wife is in her office doing her nails then working out, so we wait. Need her to open the top so I can look down under the tonneau cover.
Turned the car around to back in for more room in the trunk (2 single garage doors really suck) and it was stuck in the Jaguar logo for the third time now.
Turned off the engine and locked the car.
5 minutes later (just now) and the screen is still on with the logo. FML.
Restart the car, screen works fine.
Turn off the car and screen turns off as normal.
** Time to search the forums for this one.
Will report back when the wife is available.
Reporting back.
Wow if one could lift a 70lb battery that high, it can just be dropped in through the tonneau.
But still went in through the trunk to look.
Who knew the spare well lining just lifts out.
Took everything out. Vacuumed all three after the pic.
Then cleaned out the entire thing.
** Anything else I should do while I’m in there?
I found a vent tube on the ground side.
Assume that’s it.
There is nothing on the Pos side.
For posterity, here is the whole thing, with all carpet removed.
Gonna leave all the inserts out and get the battery replaced with the Walmart AGM H8 tmr before I have to drive my daughter back to college Sunday.
Last edited by Circumnavigator; Oct 17, 2025 at 06:41 PM.
Please consider reaching out to a moderator (Don B) to re-title your post to something searchable for future users with battery issues. You have a bad battery btw:-)
@Don B Any chance you are able to rename this thread to something more useful?
Make your life (and back) easier and make a simple ramp to slide the old battery out, and the new one in.
IIRC, this is what I did, based on tips in other threads:
1. Remove the luggage cover
2. Remove the floor panel
3. Remove the cover over the battery and electronics stack
4. Remove the angled bracket battery hold down (bottom front of the battery)
5. Put the floor panel back in
6. Lay a short 2x4 parallel to the battery
7. Start sliding the battery onto 4” wide board
8. Lay a 4 foot 2x6 or 2x8 board from the edge of the 2x4 and up and out the trunk
9. Slide the battery up the 2x6 out of the trunk
10. Remove battery (didn’t have to lift it out)
Reverse the steps to install the new battery.
Make your life (and back) easier and make a simple ramp to slide the old battery out, and the new one in.
IIRC, this is what I did, based on tips in other threads:
1. Remove the luggage cover
2. Remove the floor panel
3. Remove the cover over the battery and electronics stack
4. Remove the angled bracket battery hold down (bottom front of the battery)
5. Put the floor panel back in
6. Lay a short 2x4 parallel to the battery
7. Start sliding the battery onto 4” wide board
8. Lay a 4 foot 2x6 or 2x8 board from the edge of the 2x4 and up and out the trunk
9. Slide the battery up the 2x6 top of the trunk
10. Remove battery (didn’t have to lift it out)
Reverse the steps to install the new battery.
There was no need to remove the spare tire.
What's a spare tire? Me no have one of those.
If I can't pay someone a bit younger than I, this plan sounds good.
I will just leave all the inserts out of the trunk when I go to Wally World.
(See last photo above)
... it was stuck in the Jaguar logo for the third time now... Turned off the engine and locked the car... 5 minutes later (just now) and the screen is still on with the logo...Restart the car, screen works fine. Turn off the car and screen turns off as normal...
@Circumnavigator , not exactly the same as what you are experiencing, but 4 or 5 times now over the past 6 months I've parked my car while running an errand and when I return the infotainment screen is blank. I learned that if I turn the car off, get out of the car, double lock it using the exterior door button, then unlock and restart the car and all is fixed. I'm assuming the double locking immediately shuts down all electrics and allows the infotainment system to reset. Worth a try...
@Circumnavigator , not exactly the same as what you are experiencing, but 4 or 5 times now over the past 6 months I've parked my car while running an errand and when I return the infotainment screen is blank. I learned that if I turn the car off, get out of the car, double lock it using the exterior door button, then unlock and restart the car and all is fixed. I'm assuming the double locking immediately shuts down all electrics and allows the infotainment system to reset. Worth a try...
Yep, on my 4th or 5th thread after searching “screen jaguar logo”.
Things like the car start order (AC start then brake start, push button then brake).
Turning off auto headlights.
Turning off auto screen brightness on head unit and keeping on middle.
Your suggestion was mixed in there as well.
She seems to be holding onto 12.57v fairly well so far.
I did disconnect the pos cable for about 30s as someone mentioned measuring the battery while disconnected.
Still 12.57.
Then I ran out for gas and seems that 30 seconds reset everything. Trip odometers, all of it.
So I did the driver’s window reset.
Was wild.
Window down. Hold 10s. The idle RPMs actually dipped twice while I held the button down.
Raised the window, held 10s. Idle dipped twice again.
I skipped the passenger window.
How can resetting the window cause the idle to dip??
Last edited by Circumnavigator; Oct 17, 2025 at 09:39 PM.
Me no have one of those.