I was out for a ride today to check on the only golf course open to us so far and while driving I have a volt meter plugged into my glove box outlet. So being it's a cheap little digital cig. lighter volt gauge it read 13.4 volts throughout my hour and a half drive. So I was just wondering what you guys see if you use anything other then the torque adapter. I didn't do a compare but will sometime this week. I do have the car on a smart charger at night so I don't have any issues with that. Just askin

 

I am looking forward to hearing if the cigarette lighter voltmeter is accurate. I use on of those sometimes and am wondering if it is at all accurate.

 

That is a very interesting subject, as I had found when I connected to the ECU with my Torque app and Samsung phone.

Starting and driving the car right after the battery being charged or maintained for weeks continuously by my trickle charger I found the voltage reads to be surprisingly low while starting and driving the car for the first few miles. If I remember correctly the read was 11.9 Volts DC. It actually scared me into thinking that my alternator was NOT charging under driving conditions. That lasted for the whole drive of about 30 miles.

I parked the car and in about an hour got back into it to drive home. Now, the ECU read 14.1 Volts for the whole drive to home. That is normal, what I would expect. Your 13.4 V read would tell me that your battery was fully charged and the intelligent charging system simply maintained that voltage level, instead of blindly charging it with the normal 14V+ levels.

What I came to conclude was that the Jaguar charging system is intelligent to know when to charge and when to actually "discharge" a seemingly overcharged battery. When I removed the trickle charger that car's ECU saw a battery voltage of 13.5 Volts and apparently considered that to be too high of a "resting" voltage. More like 12.6V would be normal for a fully charged car battery while being parked and not charged. So, instead of sending more charges into the battery it actually lowered the voltage to discharge levels.

When I started the car at my remote destination, the large starting current draws (close to 400 Amps), combined with the 11.9 discharge voltages during the first leg of my trip, made it look like the battery needed charging, thus the 14.1 VDC read.

That is my theory to explain what I experienced and I am sticking to it :-).

 

11.9 volts indicates that your charger was not doing much while the car was at rest or that your battery is on it's way out.

Measuring system voltage doesn't really indicate much also as it's normal to see variations between 11 and almost 15 volts depending on several factors.

OEMs have deleted or 'dumbed down' gauge indication on most cars as many people are not familiar with what the readings indicate and what action to take.

 

The actual inherent voltage of car batteries is 2.2 Volts per cell, or 13.2 volts total. If an electrical system considered this too high and lowered the voltage to 12.9, for instance, the battery would then be BELOW the normal voltage it was designed to produce. The battery would therefore never be completely charged.

 

Correct!

 

Indeed, Jaguar dumbed down the display, relying on idiot lights only for warnings. Thus is my use of the OBDII Torque Pro app with my mobile phone to indicate vital temperatures and voltage levels in the car.

The battery was fine and is still fine today, a year after. It is difficult to explain 11.9 ECU voltage for a full 30 mile drive. As you stated, this would be seen when the alternator is NOT charging and normal loads are being pulled from a fully charged battery. Since we are not able to see the Jaguar charging logic language we can only speculate what happened from what was observed. Yes, it is possible that the logic contains a language that shuts off the charging when detecting 13.5s VDC levels (after taking off my CTEK) and not seeing a charge coming through the small charge monitoring device on the battery negative post. It could translate that as an overcharged battery. Normal, fully charged battery cell voltage is 2.1 VDC when not being charged and it would be 2.2 VDC if under an automatic float charge (CTEK) or shortly after disconnecting it.

Since that incident I do not keep my float charger ON continuously but disconnect it periodically to allow the battery to take on a normal discharges at the measured rates of about 40 mA. I have not seen the same low voltages since I'm following this practice.

On the other hand, it is also entirely possible that the charging logic simply hung up due to some electronic gremlins. After I shut the car off and started it for trip home, the charging voltage was 14.1. That is not out of the question as I had a couple of very similar hang-ups in the same '10 XKR where the infotainment system failed to shut down after turning the engine off and locking the car. It proceeded to suck the battery down to the extreme low levels of 3 - 5VDC in just two days. I measured that system pulling 1.4 amps which explains the rate of discharge. That was (hopefully) remedied by a factory TSB, by reflashing the software.

The Jaguar electrical system is, IMO, not particularly well designed, particularly when looking at my XJL which displays "Low Battery" warnings frequently, like after a fully charge and opening the car doors for a few seconds more than once. The XJL particularly draws huge amounts of currents, close to 17amps, when the two electronic dash/console screens and the computers wake up on the openings of a door. That is why nearly all XJs on the dealer showroom floors either have Low Battery warnings or have chargers attached to them constantly.