It varies. I generally don't pay attention these days, but I paid more attention when I first started using it (using the jumping points under the hood)... at that time it could take as little as a few minutes (if I unplugged for a couple hours but didn't drive it - in which case it was probably just testing the battery) to 24 hours. Depends on how long it was off the BT and/or how much driving I did in between. I have the Battery Tender Plus though, which seems to charge a bit faster than the BT Jr.

I haven't been able to take the car out much in the last few weeks due to time conflicts, but typically if I take it out for a few hours and then plug it in, it is topped up by the next time I check it... which is usually the next day.

 

I have used both the BT Plus and the BT Jr. The former takes about 24 hrs every time, and the latter takes 30+ hrs. It doesn't matter if it's a short hop or a 100 mile trip.

However, I can leave it unconnected for a couple of weeks, and it has never failed to start. The voltmeter does show much higher readings if I've left it unplugged for a number of days, meaning the alternator is charging more often.

 

I am a bit curious about this thread. I have never needed a tender for anything but my motorcycles that might sit for months at a time. Just got back to my f-type after being on vacation 8 days. No messages, no problem starting. A locked car should be able to sit for several weeks without needing a BT. Anyone having these issues with discharged batteries should insist on the appropriate repair: new battery, fixed charging system or finding low current drain.

 

I have a service scheduled for Tuesday to look at this. The past 2 days I drove the car over a 100 miles each day. First night I got home and decided to lock the car (in the garage) and not worry about plugging it into the BT. The following morning I go to get in the back hatch and it wouldn't open. Get in the car and sure enough "low battery please start car"... After another nearly 100 miles of driving, I get home and decide to put it on the BT. This afternoon I see the BT is still charging (about 12 hours after I plugged it in) and when I get in the car I STILL see a Battery low please start car message even after the BT was plugged in for the past 12 hours.

I'll let you know what the dealer tells me after I bring it in on Tuesday. I agree that a 100k vehicle shouldn't need to be plugged into the wall outlet every night like an Iphone!

 

This is my third Jag and I've never had a battery or electrical issue and if I had to plug in a tender every time it sat, I would park it at the dealer until it was fixed.

Over the winter I used to just charge it up every 4-6 weeks if it was not driven and no issues. Sometimes after this period of time it would show a low battery and the charge cured it.

This last winter I put a tender on so I didn't have to charge it every 4-6. The cars have all been custom ordered and so the batteries have been fresh.

These are large robust batteries from my experience. We have some heavy equipment here and the charging rates do very a bit from vehicle to vehicle yet the batteries are fine and last for years. .. they shouldn't need to be babied, nor should the Jags... as long as they are not constantly run down.
Lawrence.

 

This is what I would expect.

 

After letting th car sit for TWO whole days without a sigle drive, I come back to a fully drained battery. Couldn't unlock the car at all. Had to use the emergency key in order to open the door to jump the car. I'm bringing in the car tomorrow to the dealer to see what the issue could be.

https://vimeo.com/138498730

 

I'd wager it's nothing more than a dead battery.

 

I'm curious to know if there is simply a bad batch of batteries or some bad charging module out there...

 

That's what I'm hoping, and not some kind of vampire drain somewhere.

 

After 3 1/2 weeks in body shop battery was very low even though they disconnected the battery most of the time. Only took 24 on the Cetek to charge up. Started even when low.

 

I have never had a starting issue, or a low battery warning on my F-Type and nearing the 2-year mark, no matter how long I leave it unplugged. So my battery is healthy enough to continue doing it's job.

However, I'm convinced that there is something "different" going on with the F-Type charging system. I have two BT Plus units that I switch between vehicles, and as result of all the discussion here, I've been experimenting with charging times after driving each of our vehicles.

In the comparison times to full battery charges below, each vehicle has been driven more than 300 miles in one week, and I've hooked up a BT Plus immediately after the last drive (except for the Jeep). Of all the vehicles below, the F-Type has the fewest options.

• '14 F-Type: 24 hrs + (every single time)

• '13 Winnebago Tour: 6-8 hours (42K lbs GVWR motorcoach with two heavy-duty chassis batteries)

• '15 Jeep Cherokee Trailhawk: 6 hours (after sitting for 4 days unplugged)

• '15 MB C-300: 10 hours.

 

Are all of your batteries AGMs?

 

Yes.

 

I agree something is different in the F type. I've used BTS before also, and this is the only vehicle I have ever had it on the charger for more then 6 or 8 hours...

Anyway, just dropped the F type off at the dealer. I'll let you know if or what they find d. In the mean time they gave me a new XJ as a loaner. It feels like I'm driving my sofa... not a bad thing, just very very different.

 

Yes, please let me/us know what they say.

As another interesting data point, I drove my F-Type to work after sitting unplugged for 5 days. I did start it a couple of times over the weekend to pull it out for a wash and back into the garage, but if anything that would have run the battery down even more.

I've gotten in the habit of testing the resting voltage before I start the engine, and it was reading 11.7--lowest I've seen since I got the plug-in voltmeter. It started fine, and shortly after pulling out, the reading shot up to the high 13's with spikes over 14v. It stayed in the 13s during my entire 30 mile commute.

As I previously reported, if it's been on the BT for 24hrs., the resting voltage is 12.7 and drops to between 12.2-.4v as I'm driving, and I only get spikes in the 13-14 range after driving for about 20 miles or more.

What seems to be different about this car is the battery mgmt system software is programmed to only put the alternator into action when the battery voltage falls to a certain level. The other weird thing is that the resting voltage of my motorcoach after charging is always above 13v. vs. always 12.7 on the Jag.

What these data seem to suggest is that the battery management system software does not allow the alternator to fully top off the battery as I'm used to in other vehicles.

 

At first I thought maybe the warning was set just a little too sensitive, but it really started to bother me when I came out to the garage with hands full and the rear hatch wouldn't open..

So far it's never not started, but I didn't want to get to that point.

The dealer did ask me if I left the keys in the car at night. I do not. It's always locked in the garage and the keys left in the house. He definitely agreed that as much as I drive the car I should not be getting a low battery message. (10,000 miles in 4 months. ) Maybe the TX summer heat didn't do well for the battery...

 

I took my 2014 V8s in for service after getting a lot of dash warnings - Park Brake Fault, ABS Not Available, Special Modes Not Available, E-Diff Not Available. They would come up after a few short trips, then after a long trip and one more restart they would clear. A battery tender decreased the occurrences but did not eliminate them. This started the first day I owned the car and persisted, gradually getting worse as the battery got older.

Suspecting a weak battery, I bought a voltage meter that plugs into the accessory port and saw readings as low as 11.9 volts when the car was running. This was after using a tender for several months. The battery appeared to be failing.

I took it in, of course the dealer said the battery was fine. I think that is bullshit so I bought a new battery. They did a transfer module reflash which has not changed much. I paid for the new battery and now the lowest voltage I ever see is 12.3, but if I don't use the tender I do still get the same dash warnings, although less frequently. Again, they clear after one long drive and one or two restarts.

Even with a new battery and a reflash of part of the charging system it still takes a couple of days to fully charge the battery in the tender if I don't use it every day. Very stupid of jag to make a car this sensitive to battery condition.

I think the cars require a perfectly charged battery that is in perfect condition and I also think the charging system is unable to deliver these requirements. I also think that the jag engineers are overtaxing the car with too many very sensitive modules. My car in particular has every option so maybe it's even more of an issue for me. Using a tender seems to be the only thing that keeps the car happy so I will live with it. It is a shame because it definitely makes this car less satisfying to own and live with day to day than it could be. I am still waiting for a real fix to this issue. I suspect it will be a very long wait. All the recent Jag's suffer from similar issues.

 

I haven't heard anything today, but if I check my Remote Apps I can see the car is unlocked and the rear hatch is open. (I assume they are charging the battery...)

More info as soon as I get it.

 

I agree Foosh, and I would add that none of my cars show as low of a resting voltage as my jag, nor are any of them as sensitive to battery charge condition.

I think it will take the forum to find a fix for this one because from what I am seeing, the manufacturer isn't doing much. Probably we will have a fix in about five or six years at this rate. There are lots of clever people buying these cars. One of them is bound to learn its secrets.

Meanwhile, I guess I keep using the tender and hope I don't forget to unplug it every time I drive my car.