Tonight I had a dead battery when I came out of work. Had AAA jump and test.
AAA's tester noted the folowing:
1) Battery low prior to charge. (DA)
2) Battery only 3 yrs old, but checked good (Draw test)
3) Fired right up with jump
4) Charged at 13.8-14.2 at idle with no load.
5) Charged at 13.2 at idle with lights and heater on. (probally with auto front windscreen heater on as temps were low)
6) Charged at 12.5 with everything possible on, including every heating element.

When I got home I hooked up my trusty Icar, and had a look, as I felt it would be more accurate.

1) voltage at idle with all systems off, 13.5 - 14.
2) voltage at idle with everything on 12.9 (I mean everything, including the kitchen sink)
3) bumped up the throtle slightly, and up she went to 13.5 - 14.
Boy do the window heaters suck some juice !!!!!

With the Icar I looked at every voltage peramiter on every system and no issues stuck out. Including "possible over or under charging systems)

I'm hoping that this was all caused by me possibly leaving the lights on including the rear fogs while at work (5hrs), as it was daylight and snowing. I always have it auto, but needed to override it today, and maybe didnt hear the chime.
Do these charging voltages sound normal?
The last thing I want to replace is a weak Alt. The labor is going to hurt bad!!
What are the normal charge rates for:
1) No load at idle ?
2) Fully loaded at idle ?
3) Fully loaded at above idle?
Thanks
On the downside, I looked at my fuel trims, and saw that I have some work to do in the future chasing vaccum leaks. But thats for a different time. How did I ever maintain my Jags without an code/live data reader, I'll never know.

 

Your readings look reasonable from past experience. I would put the charger on overnight to ensure the battery is fully charged.

 

Hopefully it's not one of the dreaded battery drains!

 

I had a similar battery failure recently:
https://www.jaguarforums.com/forum/x...hboard-155654/

Actually, the battery was not dead but probably discharged and a christmas tree appeared on my dashboard.

The voltages you measured seem to correspond to a deeply discharged battery that is still alive.
Keeping a discharged battery for some time is however not sound for its life.

As said above, you need to make a full charge overnight, preferably with an intelligent charger, and then check voltages again before starting the engine.
You should have around 13.30 volts initially that would decrease progressively down to 13.0 or 12.9.
If it goes further down without devices on (except the lights in the boot), it may be a failing battery.

 

I just went through this with my 04 XJ8. I replaced the battery and that did not fix it. The alternator was the suspect, even though it tested OK. I replaced it and have had no more problems. I will have to say that the test reports on your alternator would tell me it is fine. Just saying.

 

Thanks for all the reassurance.
It fired right up this morning. We'll see. But now I know that the rear screen heater puts one hell of a load on the car at idle.

 

Boy, trying to crank over this car with a dead battery will really throw some elec codes. cleared them and they havent returned. Only hard codes that showed up on the dash display were:
1)dsc not avail
2)trans fault (that wasnt fun for the 15 minute ride home at 30mph and 2000rpm!) Probably would have self-cleared if I shut it down and back up, but didnt want to chance getting stuck away from home.
Now I really know how this car acts with a bad/low battery.
Also, I have been waiting for the battery to end its life, but its not the original (2006). Someone else paid the pretty penny for a OEM jag battery 3 yrs ago.
Thanks again for all the reassurance, now I have to find something else on the car to spend that money on.
Mark

 

I'm more versed in American vehicles but a 12 Volt system is just that. A fully charged battery should be 12.6 volts. Any more would be a surface charge and can be removed by turning on the headlamps for approx. 30 seconds. Any less after a charge is probably a bad battery. Depending on the battery, use or non use, it's perfectly understandable for a five or six year battery to only serve us for a three year period. A normal draw on a 12 volt system will run between 50 and 100 millivolts. For example, A trunk lamp left on can draw up to 1 amp and can drain a battery in as little as 1 to 2 days. Sorry I can't recite the math behind it.
Even though your alternator appears to be doing its job, it can also in rare circumstances be the culprit thats causing the battery drain. If there is a shorted diode within the alternator it can drain the battery when the vehicle is shut off.

 

Hmmmm......If it were me, I would try cleaning up the battery posts & terminals.