Thanks Stuart! Yes the convenience mode is what I wish there was an aftermarket reprogram or ?? to eliminate that feature. That's also a good past article on XK/XKR Battery Overview and replacement. My battery is stamped 12/20 and is an AMG quality level battery. I bought the car about a year ago so the prior owner must of recently had changed it. I normally keep it on a simple trickle charger (Schumacker brand) with leads directly to the battery but I had disconnected about 3 weeks ago thinking I would be driving it once a week or so now that the weather is nice in Ohio. In the 2-3 weeks timeframe it went completely dead apparently as I had no power at all. But I keep the car in my garage with the top down and was working on various things on the car over the course of that time, so I may have had the doors in an unlocked state several times back and forth over this time frame. I'll have this AGM load tested but I am near certain it will check good. I just need to really pay attention to locking the doors is all I can figure at this point.

 

I can’t tell you the minimum size battery needed to start the engine but , with all the electrics and computers, there is a big load in addition to the starter. A tip top battery is essential.
People have made a false floor to level the bottom of the battery with its mounting area and then slide it in. Lots of threads on installation of the battery here. I found the hold downs removal and installation more aggravating than loading the battery. And I’m old.
My two year old Interstate battery crapped out last summer. All fine, fine, fine then nothing. That surprised me as well. New, fully charged battery solved the problem.
As StuartS notes, locking the car (and storing the fob well away from the car) preserves the battery charge. Most people regularly use a maintainer.
The battery junction box with the 3 mega fuses is on the left of the battery by the negative cable. The 400 amp fuse is associated with the starter and the power + cable for the starter runs through the remote jumper post connections via isolators.

 

Thanks Mike! What does storing the FOB away from the car do to preserve the battery if the doors are locked. That is certainly one thing I was not doing as I kept the keys in the cup holder all the time. I was aware of locking the doors so i am surprised I forgot to do this, apparently multiple times as I was working on various things in the car.

 

And your right about taking them nuts off to get the battery out. That's more of pain than removing the battery I agree.

 

Here is my theory. The security system is looking for the fob even when locked. The fob tickles the security system to be ready to open the car when the fob is sensed. The constant presence of the fob increases the power draw as the security system is in the ready to open the car mode constantly. Probably not a lot of extra power but it doesn’t help the battery.

 

The Infotainment system and/or Convenience mode draws an incredible amount of power from our battery. Recently, when I was working on my car, I checked the draw when opening my door. My battery is always on my CTEK 3300 when not being driven... no exceptions. My battery was reading 12.80 at the posts before opening the door. Immediately upon opening the door it went to 12.35 volts. That's a huge draw. Now, just imagine some tech is working on your car and has the doors open on a regular basis throughout the day or days....If the car is not started or driven and this goes on for an extended period of time, I'm sure this can potentially destroy the battery. If the battery is too deeply discharged, it may not come back to it's original health and/or be ruined. That's why our electrical systems are so vulnerable. I've always been concerned when leaving my car anywhere to be worked on. It's a royal pain as well as an expense to keep replacing that 60lb battery. Something to think about. Doors must be closed and locked frequently as well as constantly hooked to maintainer. FYI...If anyone gets a chance while the battery is exposed with the doors are open for an extended period of time... place your hand over that stack to the right side of the battery.... It get's really hot!!!!

 

Hmm - interesting indeed. Well that's easy enough to address. My AGM is on 2 amp charge with a high quality for a few days and so I'll see what is shows Wednesday and go from there. I am starting to read / learn a lot about chargers and batteries in this process for sure.

 

That is very interesting about the power draw. That CTEK 3300 looks similar to the Schumaker charger I was using but yours I see is a $100 charger so it must be a higher quality charger. I literally have 4-5 chargers to chose from since I have bikes and other toys. Some are the larger sized maintainer / charger /starter type with selections for battery type and others that are the smaller motorcycle auto trickle chargers. If I do have to get another battery would I be better off with a lithium battery since it can handle up and down in voltage levels / recharges better? I see some either you or someone has a Lifepo battery which is lithium I thought. Would be interesting to know what amperage model that is if this is the better way to go.

 

This isn't correct though. It's a passive system for the remote buttons. And for the keyless system, it doesn't 'look' until a door handle is pulled or the boot release is pressed.

 

Ok… Thanks for the correction, ceejay. So it doesn’t matter if the fob is left in the vicinity of the car??

 

That would be good to know since I keep the car in my garage with the top down always (and covered) but with the FOB in the cup holder normally

 

An AGM battery does not belong in an '07. You'll get away with it but there is no BMS nor is the alternator up for the job. You will be dependant on external charging.
Similarly, lithium batteries have a different "power profile". Not the right choice for the car.
The good ol' fashioned lead-acid works best in this car. 900 CCA and charged to 12.6v. I leave my car for months on end without a charger and no issues.

 

Prior to converting to lithium, mine was fitted with an AGM with higher spec than OEM and had no issues though technically the original specification was a traditional flooded battery. Even when BMS was added in the 2010+ MYs, AGM was not always fitted from the factory.

 

Thanks again! I’m all for saving some money on a new battery if that is what I need. The alternator point could explain why I have been drawing the battery down more quickly it seems. Using an AGM and always having it on trickle charge then would overcome the lack of alternator output. Go on a long trip and it would seem that you would end up having an issue though. How do you determine if an alternator is not capable of maintaining/ restoring the charge on a battery in a car? All dependent on the amount of draw while running vs. what the alternator puts out I would think.

 

I agree on all points. The Lead Acid Flooded battery is the way to go.. 900 CCA H8 I've purchased all of mine at Walmart (Everstart Maxx) They are getting fairly expensive lately. FYI... The last few visits I made to Walmart showed ZERO H8 batteries as well as a low inventory on other batteries as well. Another shortage issue to deal with.

 

Not really, as I said I had one fitted for several years with no issue and even though not required, I've always used AGM batteries even in all of my other cars, Mercedes, VW, Infiniti, Land Rovers, other Jags, etc. They're much more reliable, less prone to discharge and longer lived than a flooded battery, they can handle discharge better and they charge faster than flooded. HOWEVER the risk with a vehicle without BMS (AGM battery monitoring system) is if the vehicle's charging system overcharges the battery or the voltage is too great, the AGM battery could be damaged. Also vehicles with BMS are not compatible with flooded batteries and require AGM due to the different charging profile.

So, for many long continuous road trips, AGM might not be best suited to your application but for short trips or infrequent use, AGM would be fine which's why it worked for me.

Make certain your trickle charger can switch between AGM and flooded, again due to different charging profiles. A non-AGM charge can easily overcharge or have voltage too high.

 

I've read several threads with satisfied owners who swapped to AGM, regardless of MY. I know the owners manual says only to use an AGM battery if it was originally fitted with one. Some of us surmised it was alternator dependent. @GGG clarified after a conversation at his dealership. The AGM was fitted to Jaguars with stop/start technology IIRC what he wrote. So the bottom line for me is, there doesn't appear to be a negative impact of using AGM over Lead Acid. I use Lead Acid but really, they are all only warranted for three years so I choose to go with cheap. I'd think different if battery weight is you concern (racing) but even there I'd look to @jahummer solution.

 

provided. again. https://www.motortrend.com/how-to/hr...a-agm-battery/
The point to be made is that the alternator in an ’07 is not “geared” to handle to handle the unique requirements of an AGM battery.
This is not necessarily an issue if you prefer to adopt a strategy of providing an alternate charging capability while she is parked. (And I can’t be bothered)

 

I used an AGM battery in my '07 XKR daily driver for over 4 years with no issues and the day I installed it was actually the day when I put the CTEK away in the cupboard so the alternator was the only thing keeping it charged.

 

Does anyone actually know what the milliamp draw should be on the battery during convenience mode after turning the car off, and what the draw is after that time for the small items such as the clock... My understanding on many cars is that we would see 300-750 milliamps initially upon connecting the negative lead for powering up capacitors / electronics... but then within 15-20 seconds this would drop to say 25-50 milliamps on a continuous basis which just maintains the clock... If I knew this, I could confirm my cars is within range. And if not, I could pull fuses individually until I found the source of the drain. I am going to hook up a digital amp meter in-between negative and the post and conduct this test when I hook my AGM battery up tomorrow. Just thought I would ask first.