Bentley GT Main Battery Dilemma
 

Hi Guys,
UPDATED: I have created the guide and it is attached here
My Bentley GT (2005, UK Model) Main Battery keeps losing charge and dies. I don't really want to go to the dealer as they are charging a whopping £400+ to replace it which is ridiculous and another Bentley dealer 200 miles away from me is asking £226 but it's to far for me.

Can the main battery be changed without going to the dealer?

Does anyone know how to remove battery? As it's got some wires attached to it.

See the pictures attached

I will also create a guide for people once I figure out how to change the battery.

https://cimg4.ibsrv.net/gimg/www.6sp...20ee15bcf3.jpg


https://cimg5.ibsrv.net/gimg/www.6sp...717a10000f.jpg


https://cimg6.ibsrv.net/gimg/www.6sp...68d036cf99.jpg


https://cimg7.ibsrv.net/gimg/www.6sp...9c0f74bdb1.jpg

disconnect both terminals isolate them so they dont touch the body and remove the battery.
Once the positive terminal is removed all the associated positive leads will flex to move out of the way

Additional advice
 

What I was told:




Make sure the steering wheel is straight and all the windows all the way up. Disconnect the battery and remove. Replace the battery. Be sure to wait 15 minutes. then reconnect the battery. Start the car up and drive the car around the block for the esp and traction control lights go off in the dash. Then roll the window down – when the window is down, hit the switch down again; then roll the window up and when the window is all the way up hit the switch up again to learn its stops. Do that for the other 3 windows same procedure above. Then pay attention to the clock - is the clock operational? When you connect the battery again the clock should go to 12 o clock first and then time should start.


Brian.
2008 GTC

Thank you very much guys for the reply. One more quick question do I need to do anything to the starter battery? Like disconnect it or anything? Or do I just leave it as it is, the starter battery is fully functional.

Many thanks again, going to order my battery soon.

I have a feeling that the starter earth should be disconnected first/reconnected last. Something to do with the pyrotechnic charge on the starter battery.

Have you considered an Independent Bentley specialist? Mine,'GT Services', is in Crewe and is brilliant.

Les.

Just checked IETIS for you. Here's what to do.

1. Switch off ignition and all electrical consumers then remove ignition key.
2. Wait 60 seconds then disconnect the starter battery earth.

You can then change the main battery. There is also mention of checking zero steering calibration so maybe that's why you need the steering straight ahead.
As well as the windows, you may have to reset the seat memories/clock, etc.

Good luck.

Les.

Hi Les,

Thanks for the instructions. I managed to get it all done. Was fun actually and frustrating lol but got there in the end.

You were right about everything it was all reset to default so had to change things back.

The battery weighs a ton or its a sign that I need to hit the gym lol.

Thanks for the help

No prob's. Glad you got it sorted.

Les.

Thankyou samy999, this thread has been very helpful.
I have a question, in the foto you have posted of your main battery, the specifications are :
3D0 915 105 G
12V 85Ah 480A DIN
860A EN

So my question is if i get a battery with more than the 85Ah for example a 90ah and 800A, is that compatible? Does any one know?
So which would be the best out of these :
https://www.norauto.es/catalog/260_M...ica-y-4x4.html
Thank you

Hi Rabent.

The more amp hours the better in my opinion. Not sure what the other (800) amps relate to though.

Les.

The 800 figure represents something like the A available in cold, or something like that, not 100% sure.
I'm going to order the correct batteries and try out this DIY. I'm relying on samy999's pdf guide.

Good news, for the moment i have replaced the starter battery which seemed and was very simple and everything works fine.
I will soon order the new Varta AGM 95Ah 850 EN which is better than the OEM 85Ah that Bentley offers.
I would also like to add to any guide of the Starter Battery that there is a narrow flexible plastic tube that comes from the car (i think is the breather for any battery fumes) that has to be plugged to one of the breathing holes that the battery has in either side.

Low battery warning
 

My main battery has been replaced recently and now I am getting a low battery warning again.
I keep the tender on all the time and it shows full charge.
Dealer told me the tender does not charge the battery on the right side??
Does anybody know why it is not set to maintain both batteries?? :(
2009 Bentley GTC

Hello GTCrewe, did you resolve this issue? I have the same problem. I used a duralast h8 agm battery and it died in a week....

Low Battery alarm
 

I believe the battery on the Right side is reason for my Low Battery alarm since I have no problem starting the car and running - Low Battery message goes out.
I think it is the original battery which is amazing that it has not failed before - 6 years is good.
I will post later when I stop by the dealer.

main battery left and starter battery right.
If your main battery drops below 10/9 volts even with a fully charged starter battery the
car will not start. this is why you keep your main battery only on charge.
If the starter battery goes flat, you put the key in turn 2 times to the left and then start the car as normal with the key. 2 times to the left tells the car to use the main battery.
I have had NO none starts in 14 months using my tender, hope this helps some of you.

I'm using, YUASA 9000, 2 x 12v 95ah 850a battery's

Barrery Types: H8 AGM (Main) | H5 SLA (Starter)
 

Not sure if you have a special car, but my 2009 CGT Mullinier uses a H8 on the rear left and H5 on the rear right. My car came with batteries from Advanced Auto Parts (BRAND: Auto Parts International).... the dealer dude was cheap.

My main battery was down to 3V (more on that later, will create a separate thread) but I was still able to start the car by turning the key left and activating the starter battery.

For those of you whose main battery drops below 10V, remember that the correct way to charge the battery is to disconnect the negative lead. Leaving the negative lead while charging caused my battery charger to think that the battery was bad and drained the battery further....

The low charge in my battery manifested in several ways....

- TPMS Module error warning
- KESSY module error warning
- Comfort System / LCD Screen constantly rebooting.
--- and finally..... massive smoking out of the engine.... I'm talking fumigator style.... I will be starting a separate thread on that.... but the short story is that when the battery voltage goes really low, the ECUs send incorrect ignition signals to the injector and coils and causes fuel and oil to be dumped onto the exhaust.

does your battery light stay on when started?

No it does not. It didn't stay on even when we had a ton of electrical warnings due to low voltage.... Go figure.

I got 2005 Continental GT, US model. Replaced both batteries with LiFePo4. Car lost about 100lb and became much quicker. No warning lights, everything works like it should. Boy it runs awesome!

car always has to be on a tender!

unclear which Battery needs replacing
 

I often don't drive the car for 2 weeks and yes, it's not ideal for the battery. Recently car would not start in normal mode, completely dead, no lights on at all. I turned the key the other way to engage the other battery and yes, car started. I charged main battery (rear left of car as you look into trunk. ) but even charging had no effect, still wouldnt start with normal key bUT did start usimg reverse key. I bought a new agm battery but when I was about to install it the car started ok with normal key start. It appears the main battery came back to life. I bought a medtronics battery tester and the main battery is showing "yellow" meaning should replace , but it wasn't red (must repalce) . I then tested the right side battery and it showed "red". Here is my confusion, perhaps someone can clarify, 1) with normal key use which battery, left or right, is being used to start the car ? 2) with reverse key use ie when car won't start, which battery is being used to start the car ? .....I thought the right side battery was the starter battery but after my test showing it to be "red" I'm now confused. I'm charging the right battery as I type. I figured out how to change the main battery and I plan to do that. 3) is there a guide to change the "right side " battery, it looks easier then the left but there are still some devices attached (pyrotechnics I think) so I'm asking how do I remove these devices on the right side battery . Thanks guys

slightly confused
 

if car doesn't start on normal key action , but does start after first Turning/reversing key to the left , then which battery is at fault ?

I have just replaced both batteries in my 2008 GT speed. There is no real issue other than the left battery is very hard and heavy to lift out of the bucket. I changed both in 1.5 hours. That includes resetting the windows, seats, steering wheel, and right side mirror. Remember that the memory reset procedure is with the ignition key in the run position engine is off. I would suggest disconnecting the right side negative then the left side. Then remove both batteries positive cables. Every thing will be safe and then reverse the procedure when connecting the new batteries. If you follow the other members suggestion you will find the procedure worth while and save $$$$.

Just a quick note: The life of a normal battery is max 5-6 years. Any longer and you are asking for problems.

use of both batteries
 

Apologies for duplication. I sent joe44 a pm but thought I'd post here also.
joe44 wrote........[ If your main battery drops below 10/9 volts even with a fully charged starter battery the
car will not start].... my question: do you mean car won't start with normal key position but will start after reverse key 2 to the left ? or do you mean car won't start period, irrespective of key action ?

Joe44 wrote ......[If the starter battery goes flat, you put the key in turn 2 times to the left and then start the car as normal with the key. 2 times to the left tells the car to use the main battery.] ....my question : so are you saying if main battery goes out your are totally dead, no options except replace but if starter batt goes out you can use main as a temporary backup ?

attachments to batteries
 

Main battery left side . There is a small box, think it's a sensor attached to the battery harness at the back . Does this need to be removed from the harness when you remove the 4 cables....if so ...how is it removed ? Is there a clip or bolt ? I don't want to force anything. ....

2nd battery right side. Also has a bunch of "stuff" on top of the battery. Do I remove this stuff and if so how exactly ? Or...does it all come off simply by disconnecting the two batt terminals ?

First, attempt to charge the battery before replacing them. Disconnect the negative lead and charge the battery until full (mine was very bad, took 48 hours). Most new chargers will tell you if the battery is bad ad cannot hold more than 70% of the original capacity. If replacing buy from Audi or VW. Aftermarket batteries just don't seem to last long on these cars. You can expect an average life of 5 years from a battery.

Main battery is left (big) and starter battery is right (small).

Once you cut off to the emergency battery (key to the left), it will always resort to using the starter battery (right side) until the charge on the main battery comes back above a threshold.. meaning, you must either charge or replace the main battery for the computer to switch back to it.

I don't recall seeing a small box... pictures will be helpful. I just followed the instructions at the beginning of the thread and it was good. It looks daunting at first, but once you disconnect the 4 or 5 cables from the positive lead, the negative lead and remove the junction box, you will have to also remove the small plate at the bottom of the battery that is bolted to the trunk. That should allow you to move the battery and lift it out.

The right side is more or less similar with fewer wires to remove and a lighter (easier) battery to maneuver.

Thanks. Here is what's happening now , I enter car and turn key anti-clockwise (I think this is normal operation) ...all dead. ..I then turn key clockwise it starts just fine. Note..I didn't turn key clockwise to then turn it anti-clockwise to start car...I simply turned it once clockwise and it started with the one turn of key. Given the above, which battery is working and which is not ?

My guess is that your main battery (left side, bigger) is dead.

FYI, turning the key clockwise is the normal operation. If the main battery is dead and you turn the key anti-clockwise, there is a relay in the trunk that will switch over to the backup battery (smaller, right side).

Once the computer switches to backup battery, the only way you can get it back to working on the main battery is by charging the main battery or replacing it. The computer senses the voltage of the main battery and switches back to normal operation automatically.

I would advice keep some paper towels near the trunk lock so that you don't lock the trunk. Since you indicate your backup battery might be on its way out, you don't want to be caught with no access to the trunk.

Emergency manual access lever is behind right rear seat.


.

slightly confused
 

Thank you. Under normal operation, both batteries working, when you start the car normally, which battery is starting the car the main left or Backup right ?

The left is the house battery, and the right is the starter battery.


There is no "backup battery", the juice from the starter battery is always live at the starter, then power is sent from the house battery to the starter solenoid via the start button or ignition switch.

Forgive me expanding your reply... under normal operation when I turn the ignition key to start the car it's the right side battery doing the work to 'start' the car ? Then, the left side battery takes over to keep car running. Did I get it right ?

Yes, The right side takes the load of starting the engine, and then the vehicle runs off the left along with the 190 Amp 2660 Watt alternator keeping both batteries charged.


Just like when you open the doors, roll down the windows with the remote, turn on the lights, or play the stereo without the engine running, or turn on the ignition and dash come to life before starting, that is all the left side supplying the juice.


.

So a week ago when my car had sat unused for 3 weeks the remote didn't work and no lights at all came on when I opened door with manual key, no life at all. from your comments this implies main left side battery was dead ? Then, car wouldn't start on normal key (clockwise) operation, does this mean right-side battery was dead too ? I then had to rotate key anti clockwise and then clockwise to.force a switch of battery to start the car and it started. This is my confusion, if car lights and remote etc were dead (main left side battery dead) and car wouldnt start on normal clockwose key operation (right side batt dead) then how come the car started using reverse key operation as we just determined both left and right batteries were dead ?

Regarding the extra equipment attached to both batteries ...pictures attached 1st pic is left side battery. The yellow mark to the left is the main battery terminal. The yellow mark to the right is part of this small box that is attached to the rear side.of the left battery. I think it's a sensor and I'm unclear exactly if / how to remove 2nd picture: this is the "stuff" on top of the right side battery. Also unclear how to remove.
https://cimg1.ibsrv.net/gimg/www.6sp...fa00fa238f.jpg


https://cimg1.ibsrv.net/gimg/www.6sp...722aaa4c12.jpg

I am sorry to say but, you are really not grasping the operation here, who is "WE", I did not determine that "both batteries were dead", if both were dead then it would never have started, UNLESS you charged it or jumped it, which you have not said, SO, Please follow me here :), when you tried to get in the vehicle and all was dead and no start available because your left {HOUSE BATTERY} was dead, you turned your key CCW to activate emergency start, this then sent power form the right {start battery} which obviously had juice to the left {house battery} allowing now for juice to flow to the vehicle and supplying all circuits with power, you then turned the key to the right and she started, the SAME would be if the right {starter battery} was dead, then you would have gotten in the vehicle via remote and all would seem fine as far as lighting and dash, BUT you would have a no start condition, you then would have turned the key CCW to send power from the left to the right, I believe that the misconception some people have is that it switches to one battery during emergency start, that IS NOT the way I see it, look at my GT build thread and see why, the way I see the setup is the emergency mode puts both batteries in Parallel, NOT series, but Parallel, with parallel you still have 12 volts [and double amperage with two good batteries], were as with series you would end up with 24 volts [the amperage of one battery] and a fire.


I hope this helps, now onto your next post.... hilarious

When you loosen the positive terminal with the yellow mark as you have pictured, then that whole unit with everything lifts off of the left battery,
as to the right battery, you loosen the nuts in the red circles and remove terminals from battery, and at the same time you pull toward you the tab in the green box and lift, this will get those pieces out of your way, in the purple square is the yellow connector box for the pyrotechnic device shown in the purple oblong, you DO NOT need to touch these, just disconnect the terminals and lift all together, in the blue oblong is the battery parallel solenoid that ties the positive cables from both batteries together during emergency start.


BE SURE TO FOLLOW PROPER PROCEDDURE FOR BATTERY R&R, RIGHT NEGITIVE OFF FIRST AND ON LAST.


.