The following is just my opinion based upon experiences and how I solved a problem with my own personal Ford GT. I am sure others may well hold different opinions.
I have kept note of all the threads related to battery failures and gauge problems, and as a result been very carefull in keeping my car on a battery tender when stored longer than one week.
Last February, Shelby Smith put a new Ford GT specific battery from his Ford dealer in my car prior to my purchase. So my battery was only one year old. This is the first winter that I have stored my car, but even with the tender on it, I was concerned. On Friday, I decided to check the gauge response and turned on the key. As I feared, the Fuel Gauge and Volt Meter were slow to respond and shortly both gauges fell to zero.
So I then decided to try to start the car. As I suspected, the starter solenoid would only try to engage the starter and then kick out. Note all this was happening with a one year old Ford battery that had always been on a tender. I actually checked the battery voltage prior to trying the gauges and it was 12.69 volts. After trying to start the car, the voltage was 11.55. Within five minutes on the tender, the voltage was back up to 12.79. No low battery will recover this quickly just on a tender, so the battery itself had to have failed.
Obviously, the conclusion was that the battery had gone bad in spite of its care and age. I have had some experience with Optima batteries in the past, and unfortunately, most of it has been bad. I have had clients specify them to be installed in vintage rally cars and we have found they have actually had the cases crack open due to the vibration from the car. This has never happened to a regular battery in any of our vintage rally or race cars. I have also had Optimas fail with very short lifespans in the past.
So I set out to find if I could replace the factory battery with a standard battery. A little research a my local discount store revealed that the Optima used in the GT is basically a Group 34 or 78 size battery, and is only rated at 540 CCA as stated in the Ford GT Shop Manual. I was able to find a Group 78DT (dual terminal) 850 CCA battery (6 year guarentee, $69.99) that I thought might fit in the original battery box.
By the way, you can remove the battery without having to take the chin spoiler off the car as stated in the shop manual. Just loosen the battery holddown bolt ( the 8mm hex that stands verticlly behind the center of the battery. With the cables disconnected, you then can pivot the battery up at the front and lift it clear of the battery box and car.
After getting the new battery home, even though it was slightly larger than the Optima, I was able to just fit it into the box without any problems. The only issue is related to reinstalling the luggage compartment tray. The top terminals on the Group 78 DT are nearer the center of the top of the battery than those on the Optima, so the battery cables are now located slightly ( a couple of inches) rearward. They now just contact the bottom of the tray when it is installed. There is no electrical issue here, as the tray is plastic and the cables have insulator covers on them also. All that is required is to install the lower front plastic attaching screw first, so it holds the tray down when the other three screws are inserted. You will find the tray will be slightly higher in the front, but the trunk lid easily compresses it when closed. After it sat overnight, the trunk closed completely normally.
Personally, I feel much better about my car electrically. I now have a proven, reliabile battery of significantly greater starting capacity, and have some faith that when kept on a tender, it will keep the voiltage up to where the chance of gauge problems due to low voltage will be minimized.
I have kept note of all the threads related to battery failures and gauge problems, and as a result been very carefull in keeping my car on a battery tender when stored longer than one week.
Last February, Shelby Smith put a new Ford GT specific battery from his Ford dealer in my car prior to my purchase. So my battery was only one year old. This is the first winter that I have stored my car, but even with the tender on it, I was concerned. On Friday, I decided to check the gauge response and turned on the key. As I feared, the Fuel Gauge and Volt Meter were slow to respond and shortly both gauges fell to zero.
So I then decided to try to start the car. As I suspected, the starter solenoid would only try to engage the starter and then kick out. Note all this was happening with a one year old Ford battery that had always been on a tender. I actually checked the battery voltage prior to trying the gauges and it was 12.69 volts. After trying to start the car, the voltage was 11.55. Within five minutes on the tender, the voltage was back up to 12.79. No low battery will recover this quickly just on a tender, so the battery itself had to have failed.
Obviously, the conclusion was that the battery had gone bad in spite of its care and age. I have had some experience with Optima batteries in the past, and unfortunately, most of it has been bad. I have had clients specify them to be installed in vintage rally cars and we have found they have actually had the cases crack open due to the vibration from the car. This has never happened to a regular battery in any of our vintage rally or race cars. I have also had Optimas fail with very short lifespans in the past.
So I set out to find if I could replace the factory battery with a standard battery. A little research a my local discount store revealed that the Optima used in the GT is basically a Group 34 or 78 size battery, and is only rated at 540 CCA as stated in the Ford GT Shop Manual. I was able to find a Group 78DT (dual terminal) 850 CCA battery (6 year guarentee, $69.99) that I thought might fit in the original battery box.
By the way, you can remove the battery without having to take the chin spoiler off the car as stated in the shop manual. Just loosen the battery holddown bolt ( the 8mm hex that stands verticlly behind the center of the battery. With the cables disconnected, you then can pivot the battery up at the front and lift it clear of the battery box and car.
After getting the new battery home, even though it was slightly larger than the Optima, I was able to just fit it into the box without any problems. The only issue is related to reinstalling the luggage compartment tray. The top terminals on the Group 78 DT are nearer the center of the top of the battery than those on the Optima, so the battery cables are now located slightly ( a couple of inches) rearward. They now just contact the bottom of the tray when it is installed. There is no electrical issue here, as the tray is plastic and the cables have insulator covers on them also. All that is required is to install the lower front plastic attaching screw first, so it holds the tray down when the other three screws are inserted. You will find the tray will be slightly higher in the front, but the trunk lid easily compresses it when closed. After it sat overnight, the trunk closed completely normally.
Personally, I feel much better about my car electrically. I now have a proven, reliabile battery of significantly greater starting capacity, and have some faith that when kept on a tender, it will keep the voiltage up to where the chance of gauge problems due to low voltage will be minimized.
