Replacement CTEK MX5
 

Check the battery voltage again and see if you need to charge it. Also put the Ctek on another car and see if you get the same results. If so send it back and if it is OK then your Jag battery might be bad or the way you hooked it up needs to be looked at. Let us know what you find out.

My CTEK 3300 is less than a month old and it is defective. The tender starts out charging with a solid red charge light the switches to green. It's fully charged. Then the CTEK starts flashing red continuously with the green light solidly lit. It's my understanding this is not normal. So, I'm sending the sucker back for warranty work. BTW, my battery is less than a year old. Good luck to the OP with his issue.

Is your CTEK connected directly to your battery's positive and negative battery terminals? If so, that's incorrect.

For 5.0L models, the negative CTEK terminal must be connected to a chassis ground. Otherwise, the Battery Monitoring System won't work properly.

According to the CTEK Manual the flashing red light should not constantly flash. An occasional flicker means the battery tender is doing its job while the flashing light could be a possible fault in the tender. At least that's what the CTEK Tech guy told me. He also told me to send the thing in.

My CTEK has been hooked up directly to the battery for almost 2 years without any issue.

You're playing Russian roulette with your 2010 XKRs charging system by connecting the negative CTEK terminal to the negative battery terminal. That's contrary to what Jaguar recommends.
https://cimg8.ibsrv.net/gimg/www.jag...c09e6581ba.jpg

Attached to the negative battery terminal is a Battery Monitoring System control module that is linked to the ECM . If you connect the negative charger terminal to the negative battery terminal you risk damaging that control module as well as the ECM. The negative charger lead should be connected to a body ground to bypass that control module. This applies to 5.0L X150 models.

For details, see:
https://www.jaguarforum.com/showthread.php?t=88788

Great Documentation
 

Thanks Stuart for providing the documentation below. It's an excellent resource. I wish had seen it earlier today so that when I was topping off my battery I could have corrected my install. I did figure out a way of checking the fluid level by using an inverted glass eye dropper with the rubber bulb removed. It was relatively easy to see exactly how much liquid there was above the plates by dipping it in, holding my finger on the end and then pulling it out enough to look.

Documentation I moved the negative lead off of the battery terminal today. I didn't find a body mount point to secure the ground in the area indicated, (I have a convertible,) so I had to opt for next best ground I could find which was on the battery hold down with a couple washters sandwiching the connector. A zip tie and tidy routing for the leads keep them out of the way. Buttoned up the trunk after. Thanks again Stuart S, the documentation you provided was helpful to understanding the problem and how to solve it.

I'm pretty sure that you can attach your CTEK to the remote battery terminals in the trunk (boot), instead of attaching the red positive lead directly to the positive battery terminal and trying to find a chassis ground. I know that the remote battery terminals work for charging a 4.2L because that's how I attached my battery maintainer using the alligator clips.

The positive remote battery terminal is in the trunk on the left side behind a black plastic panel, and the negative remote terminal is in the spare tire compartment towards the rear of the car and near the center. For details, including photos, see: https://www.jaguarforums.com/forum/x...lay-ups-73471/ and my posts ##17, 18, and particularly #21 with photos.

I attached my negative wire to a screw on the chassis that holds the modules to the right of the battery.