A little background first; My 2010 XKR has a fairly new (non AGM) battery, about a year old. I changed it out because I had the opportunity for a free replacement. Also, I have a maintainer hooked up ALMOST religiously, sometimes I forget, but also I don't let 'er sit for more than a week without driving.
So anyway, I unplugged my CTEK (indicated full charge) and took a one hour drive on the freeway, stopped for about an hour, then a one hour return to home. Parked the Jag, then got back in about an hour after that and of course, the Display started flashing on the grey "R" screen. That lasted about thirty seconds and then the HOME screen came on as normal. I didn't think much so I took my little shopping trip, two miles round trip with a ten minute venture. Everything was good upon startup at the store.
This morning I take a look in the garage and I see the Flashing "R" display. Car locked, but I had neglected to hook up the CTEK. The smart key nowhere near the vicinity.
Now, I have a full sized battery charger hooked directly to the battery with 2AMP charge rate selected, but the gauge indicates 9AMP. I switched the rate to 10AMP and the gauge shot up to probably almost 20AMP. Weird thing is, the car started perfectly fine this morning, tho the display won't stop flashing even when running for a few minutes.
So anyway, now I sit waiting for a supposed "Full Charge" on a battery that should never have been flat in the first place.
I really don't want to change the alternator, but I can't see any reason this could be the fault of the battery.
Ideas? Comments? Post a pic of your hot G/F-Wife???

 

Get one of those inexpensive volt meters that plug into the acc. socket and see what the voltage is when running. Other option is the Torque pro app or another app that reads data from the OBDII port. Here is my values which I think is normal. My 2012 is hooked up to a smart charger every day . I have a digital volt meter plugged into the Acc. socket in the glove box with an extension on it and it sits on the center console. After I unplug my Sears smart charger I open the door and the meter turns on and reads 12.5V. I get in and start the car and the meter reads 13.7V. I drive away and it stays at 13.5-13.7 V all while driving. It works the same way every day that I drive it.

 

I have a good Multimeter and the Torque app, but I wanted to make sure the battery was charged before I checked it, just in case. I looked a bit ago, and the Sears Smart Charger I have indicated Full, but on a hunch I disconnected it for a few seconds and plugged it back it. Now it's back to charging at 4 Amps. Display is still flashing. Now I'm to the point to do what jagtoes outlined above.
One of those cheap volt meters for the power port would be cool regardless.

 

Even if your battery isn't charged completely, your alternator should put out 13.5-14 volts while engine is running.

 

Yep, using both the Multimeter and Torque, running voltage is 13.3-13.8 Volts, so a good alternator. The battery still has only 11.8 volts after charging for over six hours, so I'm gonna replace it with an AGM. Since the dead one is less than a year old, I get 100% credit towards the new one.
But still, does anyone know how good these alternators are supposed to hold up? I did a quick forum search but came up empty.

 

Sounds like a dead cell. Do a load test on the battery just to see how it went bad.

 

Dead alternators are a real rarity.

 

If you don't have >12.6V after the battery has been charged externally, it's dead.

Also I would expect to see over 14V while the engine is running, more like 14.2-14.3, although the voltage at the OBD socket will likely be 0.1-0.2V lower than what's at the battery, maybe 0.3V lower since it's in the boot and longer wiring to the dash.

13.3V sounds low to me...check the running voltage again when you put in the new battery.

There was a thread here in the X150 section on this exact topic a while back...

 

AGM's are a bit harder to charge.

The absolute best thing you can do with a new battery is to give it
a full, deep charge before connecting to the vehicle.

With a Group 49/H8 battery, this can take three days.
Certainly two. Never one.

Well worth the trouble.

 

It would seem my nearly new Sears Smart Charger flunked high school. After 12 hours and a "Full Charge" indication (which was a whopping 11.8 Volts) I brought it in to exchange, but of course O'Reilly's did a check on it after three hours of 25 Amp charging. Well, it came out at exactly 13 Volts (13.00) so a no-go on an exchange.
To continue, I again hooked it up for ANOTHER 24 hours (which is now about 48 total) and it's now 13.1 Volts.
Evidently, a good battery and a good alternator. So, what the heck with the low voltage right after a long trip??? Freeway speeds (of course with a few bursts ) for two hours. Of course with the top down, stereo up, windows up, A/C set comfortably at 72F and seats on cool. Still, that shouldn't have been a problem. Guess I'll have to try again with everything on and use my Torque to check and graph the voltage.
I haven't reinstalled the battery yet, but expect no Flashing "R" screen problems, for now.........