Hi Jag family, so on my 03 4.2L I've been measuring voltage and I'd like to understand at what point an aging battery ought to be replaced. I have zero problems but I know its getting close to needing replacement.

In my case after 24hrs+ I measure 12.13V. Measured 10+ times on differing days and different temps. Even after 4-5 days of non-starting it'll measure 12.1x. Even turning the ign 1 on / off & lights on/off it's still 12.13V
I plan on replacing it this summer. But at what point is it overtaxing other electrical parts? (especially the alt).

Since I plan on owning the car for 4yrs+ from now I don't mind putting a premium battery in it. Any suggestions?

 

Good question. Wish I had a good answer for you.

From what I've observed, there doesn't seem to be any permanent harm from letting the battery age until you get the fault messages for the parking brake/DSC/cruise control. Once that happens, if the battery was the reason, just replace it. You won't be stranded due to those fault messages.

But to be proactive? (Bingo!) Heck if I know. It's tricky to correlate a voltage reading to overall battery health (not just state of charge). There are so many variables.

If forced to answer, I'd suggest getting a capacitance style tester. I have an Ancel BA101 and am very pleased with it:



A friend has a Lexus, which is apparently also very finicky about battery condition. After about three years, he removes that battery and installs it in his pickup, which doesn't seem to care. He then installs a new battery in his Lexus, and trades in the old battery from his truck. He likes the peace of mind (his wife drives the Lexus). I used to think he was nuts, but now see the wisdom of his approach. He's still getting about six years of service from each battery, an average number, but always has a newish battery where it matters most.

 

Over on the "British" Jaguar forum, it is commonly held that anything less than 12.2 volts at starting can trigger faults; I know that 12.11 volts did so on my 3.0 S-type.

I believe that the 4.2 has a superior charging system that allows for better compatibility with AGM style premium batteries. As I also recall, there are only a handful of companies that actually manufacture car batteries and the huge variety of name brands out there are for the most part distributors/re-sellers of their products.

 

I've always had excellent results with NAPA Premium. It's all I buy anymore, for all of my vehicles.

Unlike many of the big chains, you will find a NAPA store in many smaller towns, too. We travel a lot and I like knowing if the battery were to fail in East Podunk, I could easily get a replacement.

 

Thanks for the replies. I think I'll replace it in about a month or so.

btw, I used to use NAPA when I lived elsewhere. We have one in this town but they are not open when I'm off work. I think they are more of a machine shop than a retail store.

 

You have a NAPA that is also a machine shop? Any kind of local automotive machine shop is getting to be as rare as hen's teeth. I think you need to change your work hours to take advantage of this, even if it means getting a new job.

 

I like the old fashioned carbon pile load tester....do it about 5 times in a row, allowing a brief cooling between loads...i have an old delco-remy one that belonged to my dad...he had a diesel repair shop...it can pull 1000 amps if need be...thing weighs a ton and smokes like hell....now i just showed my age

 

I have a carbon pile load tester, too, but can't remember the last time I used it.

Here's what else I have:

1) A vintage Schumacher BT-100 resistive load tester, aka "Toaster":


https://www.batterychargers.com/en/p...ry-load-tester


The same basic model has been in production for years. This tester has a 100 amp test load. You hold the spring-loaded switch for 10 seconds and you watch the voltage under load. This tester has some limitations, and the battery must be fully charged before testing, but it is still very useful. However, this very simple to use, and easily portable, unlike the carbon pile unit.


2) An Ancel BA101 capacitive tester, mentioned in an earlier post:


Ancel BA101 Battery Tester | Ancel Scanner-Auto OBD2 Scanner


This one doesn't apply a resistive load like the toaster, instead doing some electronic magic based mainly on capacitance. The battery need not be fully charged for testing. It determines both the state of charge and overall battery health. This one is far more accurate. It also has some other functions such as the ability to accurately check an alternator for AC ripple.


Here's an excellent article from a trade magazine, explaining some of the variables for testing batteries. Well worth a read, as it also talks about a battery's VERY important function as a giant capacitor, something that is rarely considered:


https://www.motor.com/magazine-summa...tery-of-tests/


Curiously, note how the author says the toaster has no place in a modern shop. I sort of agree, and if I could only have one tester, I'd go with the capacitive style. Still, I like to also run the test with the toaster, just being mindful of its limitations. Also, the capacitive tester I have is a budget entry-level model. A professional shop (the intended audience for that article) will typically have a much more robust pro-grade model.

Even with all this fancy equipment, it's still kind of a black art to determine when to preemptively replace a battery. And for what I've spent on test equipment, I could have simply purchased several batteries, lol. I like my friend's routine of a new battery in his persnickety car every three years, and transferring that mid-life battery to his pickup.

 

I agree Karl, battery testing these days is a fine art.... remember when group 31 batteries took 3 men and a boy to lift into place.....now that was a battery...2 of those in series and you could start anything and do some welding on the side

 

Since I maintain and work on at least 4 cars directly and help others.. I ordered the Ancel BA101.

I also did some research as well as talked to test engineer.
- 12.2+/-0.05 V is the testing spec for life cycle testing.
- 600 cycles (its a complicated cycle) is how to test life
- There is a battery factory in the US that may or may not make batteries for us.
- When V is to low odd stuff starts to happen. (seemed to be a common problem when cars started gaining ECU's to control everything under the sun. The "newer cars" have countermeasures for this)
- Batteries should have no less than 75% of the electrolyte after life cycle testing. (we weigh them before and after testing)
- East Pen web page shows the brands they produce for the H8/LN5 battery that is spec'd for the Jaguar. Of coarse we don't know if each retailer has specifications for the brand they sell. But I suspect sourced from East Penn they will have decent quality no matter where they are sold.

 

Groovy! I hope you like it. I'm very impressed with mine, especially when you consider the purchase price.

When testing a battery, you will notice you have to select if the battery is installed or all by itself. When testing an installed battery, I think the tester makes some assumptions about how this will affect the test results. For giggles, I tested an older battery (on a different vehicle) using both modes. With the battery cables installed, and the appropriate mode selected on the tester, it showed something like 35% healthy and said to replace it. With the cables disconnected and the mode changed on the tester, it came back around 55%, which passed. If this one example is accurate, I'd suggest doing the installed test first for simplicity (no need to undo the cables), but if it fails, test it disconnected for greater accuracy.

 

Thanks Karl, will do and I'll report back

 

I recently replaced my battery and got an Interstate battery, group 49 is the proper one, for my S Type, they keep their batteries charged up, most places don't. The one I replaced was probably the original Jaguar battery. Sixteen years was pretty good service from it. My voltage was barely 12 volts like yours, but was also making the computers senile, setting off faults and finally the gauges were going all over the place and the car wouldn't turn over. With a new battery and going through the reset procedures in the owner's manual, repair manual and those mentioned here, it drives like a new car, well almost. If you need I can give the specifics. Drive the car for about 300 miles before using the S button to help the car relearn it's parameters too.

 

Interesting. I've been eyeing the interstate battery. I've never bought one due to the cost.

My plan is to replace it the first week in July.