Back on the 2010-2015 5.0L charging system. I'll assume that all of the Jag models may have a similar charging system but back to my 2012 XKR. As I mentioned a few posts ago I had my alternator replaced last month because it appeared to not be charging and the dealer verified it and replaced it. I had also had time to review how the charging system works as it is not similar to the earlier MY cars. The short answer is as some know the alternator voltage output is controlled by the ECU. This being the case you do not see the old 14.2V as you are driving. My observations are as follows and my battery is a full charge from my smart charger. Battery float charge is at 13.7V. Remove charger and voltage slowly drops to 12.8 and holds. Start car and voltage goes to 13.5V. Start driving and it will stay at 13.5V while engine is under load and at idle. Now the interesting part when you are cruising say at 55 mph (or any speed) it stays at 13.4-13.5V but every time you let off on the gas or coast it goes to 14.4V and will stay there until you hit the gas again then it returns to 13.4V. I have put 200 miles on the car since the new alternator and it does this all the time. Seeing how this functions I no longer need to put the digital volt gauge in the ash tray. I also think that a volt gauge would keep drivers confused as the needle would change a lot during normal driving. I assume that is why they only put a water temp gauge and not a volt gauge in the F-Type. Just my 2 cents and I'm over this concern.

 

Sounds like a generator on Prius????
These Kats are just too skittish at times...

 

Nothing on these cars (or other modern models) is simple anymore

 

Sounds like the S-Type, where the car itself is in effect a smart charger and helps the battery to last a lot longer. We've had more than one 11-yr old battery.

 

I think that the reason that the voltage goes to 14+ upon letting off the gas pedal because, according to the Jaguar gas-saving intelligent system, that is FREE POWER. While at 13.5 the battery is not effectively charging and thus not effectively placing a load on the engine, at voltages over 14 it is charging. So, they take advantage of the deceleration inertia to place charges back into the battery.

Having thought that I had Jaguar's intelligent charging all figured out, I took my wife's 2012 5.0 XF for an extended, multi day drive while using my OBD II to monitor the voltages. So.... there was none of the voltage fluctuations there that I see regularly in my XKR! It sits solidly in the 14+ range at all times. Go figure...

 

SWMBO's Beemer operates in a similar manner, the battery gauge swinging well into the charging zone while decelerating.

I had a brand new Mercedes GLA 250 for a few days last week, it gives 'credit' on an economy gauge for storing energy.

 

Nothing seems to be simple anymore.. did you know that BMW are dealing with a pretty major charging problem on their N63 V8 turbo powered cars, that evidently relates to a not so smart, smart charging strategy.
http://http://www.roadandtrack.com/c...ns-bmw-n63-v8/
How long will they take care of owners by replacing batteries, maybe why XK owners find the need to have battery maintainers connected? Although our 2007 has been fine thro' its 2 summers with us without one..
Regards