Sure we are.

As you are someone whose posts I invariably enjoy and learn from, I was surprised at your response that's all. I freely admit that my technical know-how is a lot less than many members here, which is why I follow these forums so intently, because I am learning a lot about these beautiful cars we all enjoy so much. Occasionally, when I can, I like to give something back in return for all the help I regularly receive and one way for me to do this is to comment on my personal experiences with my own Jaguar. It is less to instruct or advise (I am in now way qualified for that!) but just to give a different perspective, or 'one person's' view on something. I was in no way challenging your own comments in this thread, and if it came across that way, then I apologise to you.

The good news is that I have now learned something that maybe should have been obvious to me, but wasn't: namely that reading the voltage off the car's onboard systems, instead of directly off the battery, is, ipso facto, not the most sensible way to determine battery health, since those systems themselves will cause the reading to be lower than when measured directly off the battery itself. In that sense, my reading of 12.2 / 12.3 with the ignition (and its attendant systems) switched on, may be perfectly OK, and if I tested directly from the battery terminals instead, i might get a much 'better' reading of voltage. Either way, my battery isn't causing me any problems, so I am happy.

Having said that, we can now, I hope, move on and put this behind us. So much communication is non-verbal in normal life, and clearly, on a forum, that aspect of communication is entirely absent, which can lead to misunderstandings, which is what I think has happened here.

 

Thanks and I apologize. Yes I was being an ***. I was having a bad day. No excuse for being a jerk so thank you.

Back to DGL's original post which looks like it's been fairly well beaten to death but to summarize, resting voltage of a battery is best tested, disconnected. Load tests are easily done by pretty much any auto parts store for zero cost. 12.6 volts resting is fully charged and anything less is a bad battery. A load test showing anything less than 9.6 is reflective of a bad battery. These tests are done at the battery.

The link Jahummer provided in post 32 is a quick and easy read. As to why your ADU and torque pro are showing less than optimal voltage (or I should say different than Stuart's and mine in this thread and others) appears to apply to the 5.0 and "may" be related to the BMS, I dunno and can't speak to it.

Bottom line is that he's indicated he doesn't have a problem but was curious about the "seemingly" low readout. If he were to do a load test and resting battery voltage check, he would know his battery's condition and then can use the ADU as a guide to what is normal output for his car. That's what I do with the readout on my head unit. He's also going to pull it to check its age once he stores the car.

As an aside, my 05 XJ had a gauge but it, like many modern cars was nothing more than an elaborate idiot light. It showed steady when everything was operating correctly but didn't reflect that actual voltage output, or so I was told by one of the techs on this site (I think it was Brutal).

 

All good.

My X Type has a temperature gauge like that. I just reads dead centre, like a switch would, on or off, rather than the actual temperature. As you say, it's a glorified idiot light. Looks good though

 

Well I stand corrected. I checked battery voltage with OBD and VOM on terminals on both the 4.2 and the 5.0 w/BMS and the difference between OBD and VOM was only about .2 volts.

 

But the terminal measurement was with the same load as when measuring at OBD, correct?
What was the difference between load and no load, measured at the terminals?

 

Yes same for all 4 measurements, ignition on but not with motor running.

 

My 13 XKR consistently reads 12.2 at rest off the cigar lighter. When running it reads anywhere from 12.9 to 13.5 depending upon the situation. Like Barnsie I never have any trouble and my car is on the CTek every night at home. When traveling it is not on the CTek and the same readings prevail.

 

Weirdly the coldest morning in my part of the UK yesterday and needed to take for a wash so dropped daughter to school. Passenger door frozen so she had to curl up in the boot*

But was getting Ralph's readings of 12.9 -13.5v with heated wheel/seats/stereo/lights/screens/blower running with lights on.

Highest Ive ever seen my ADU read and it's not been plugged into CTEK since last weekend?

Did notice tyre spin though, so have disconnected DTUK pedalbox and power control unit which improved things markedly. Winter set of rubber going on next week and will be gummi pfledging the door seals

* Joke, pushed the door from inside

 

Pulled my battery today. It is dated A5 which translates to January 2015. It's an Interstate ba3.


So it is 6 years old. Could this be why by volts only show 12.2 to 13.4--normally 12. 4? The battery tested out fine.

 

You sure did get a good deal on THAT one.
Interstate, Delco, Walmart, Everstart...... all made by Johnson Controls.

Okay, I just reread your post more carefully.... you first say JAN 05, then say "six years old"... so is the JAN 05 a typo, or the "six years old"???

 

Yes, should be 2015.

 

Ordered new Interstate AGM battery. What should my regular volt gauge reading be with the new battery? I got a great deal on an AGM, only $40 more than the flooded standard MTP 49/H8. Although, I have experienced no problems, driving on a 6 year old battery in a Jaguar it is looking for problems. I hope the AGM is beneficial and does not cause problems.

 

AGM will not cause you any problems. Make sure it's fully charged before you install it - EDIT - AGM should read 13 volts with a voltmeter. See this thread if you're curious about the AGM. Graham got clarity on the TSB that references AGM.
https://www.jaguarforums.com/forum/x...w-long-236204/

 

The new AGM Interstate battery is in my garage being charged. When I picked up the battery and returned the old standard flooded battery the sales rep noticed the side had a slight bulge, most likely caused by freezing from the previous owner. Although, the old battery performed perfectly well causing no problems, a 6 year old battery is due be swapped out. I hope the AGM battery works out well. I called my dealer and they tell me the BMS needs to be reset. I'm wondering if my Autel AP200 OBD2 scanner will suffice to do the job. I've used the Autel AP200 to put the EPB in service mode before taking the battery out to replace my brake pads and I could hear the rear EPB motor working. However, the Autel AP200 also comes with the option for BMS. I'm not sure if it just resets itself or reprograms it for either a standard battery or AGM battery. Since I'm changing to an AGM type battery do I need to have the BMS reprogrammed or is a simple reset sufficient? I don't have a battery currently in the car and will not install the new battery until I complete replacing the rear brake pads with ceramic pads, which should arrive Tuesday, so I can't try the Autel AP200 tool to see if there is an option to set the battery as AGM or flooded.

 

BMS reset is one of the features of the Auto so what do you have to lose? It'll work or you're heading to the dealer. Worth a shot imo.

 

After installing the new AGM battery over the winter I've had the opportunity to have the car out several times. I reset the BMS with my Autel Ap200 and over the last month have not put the battery on a maintainer. I understand after reseting the BMS the BMS allows the battery to be safely depleted before charging to adjust to the new battery. The car works absolutely perfect, like new.

I observed the ADU voltage meter shows 13 to 13.4 when I take my foot off the accelerator. As soon as I slightly press the accelerator it shows 12.2 to 12.4. The ADU will also display 13.2 to 13.4 on over 3.5K acceleration. At rest the ADU displays around 12.4. Just thought I would mention this.

 

You have a problem! My ADU shows 14.4 as soon as I start the car and stays there til I shut it off. Think your alternator is on it's way out.

 

he as the 5.0 his car is supposed to charge the battery at different rates

 

Sounds to low to me! :-)

 

I have a 5.0 XJL. It normally sits around the 14 volt range, but it will vary, sometimes going as low as what I would consider "too low" in a vehicle that didn't have the BMS.