changing the battery


dr914

GT Owner
Feb 11, 2009
179
Marietta Georgia
well after 16 years my optima 25 finally failed. I looked through the threads but did not see anything about maintaining the control unit memory while replacing. Do I need to plug a battery into the cigar lighter to maintain while changing?
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
3,791
It's not that big of a deal to "lose" the memory UNLESS you need to smog the car shortly after battery replacement. Replacing the battery will cause all of the monitors to be reset and you'll need to go through some drive cycles to get them "set" again.

However, the OEM charger or an aftermarket float charger connected to the the cig lighter should be sufficient to retain the ECU's memory as it is direct-wired and not ignition-switch wired.
 

Howard

GT Owner
Mark IV Lifetime
Apr 26, 2007
1,031
Florida/North Jersey
Careful there. Most battery maintainers need to "see" a threshold battery voltage or they will shut down.
 

dr914

GT Owner
Feb 11, 2009
179
Marietta Georgia
I was thinking about plugging in the 9v that we use for our porsches to maintain some voltage before changing, rather than the Ford battery maintainer I had been using to keep the battery up. Is that good?
 
  • Like
Reactions: viva gt

viva gt

GT Owner
Sep 15, 2010
408
toronto canada
Like one of these??
 

dr914

GT Owner
Feb 11, 2009
179
Marietta Georgia
yes exactly
 

twobjshelbys

GT Owner
Jul 26, 2010
5,341
Las Vegas, NV
I posted this somewhere before, probably in one of the battery topics.

Plugging the Ford supplied tender into the charging port inside the passenger compartment worked for me. I put an OBDII reader and read the system readiness status before and after and everything stayed.

However, be VERY careful about the positive battery cable! Take it off and wrap it completely in electrical tape. You don't want it short against a ground and it is highly likely during the changing process that it will!!!

I don't know if 9V is enough to keep the system alive.
 
Last edited:
  • Like
Reactions: analogdesigner

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
3,791
Careful there. Most battery maintainers need to "see" a threshold battery voltage or they will shut down.
That's a very good point! The OEM Ford GT is a "dumb" charger just blindly supplying 500mA, so it will work. But, smarter float chargers may not work as you accurately point out.
 
  • Like
Reactions: analogdesigner

gtjoey

Keep Smiling - GT Owner
Mark IV Lifetime
Oct 14, 2005
3,414
No you don't need it on this car...
You were VERY lucky you didn't lose a gage.
Well its a simple swap. Once its in run the car up to 50 miles to reset the evap control box.
Theres nothing else to reset.
gtjoey1314
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
3,791
You were VERY lucky you didn't lose a gage.
There is NO known cause of the gauge failures. One theory is electrical, another is corrosion of the fine needle movement with needle "stickiness" often being a predecessor to failure.

GT monitors can often be reset within 50 miles - but only if you really know the drive cycle.

Evap monitor setting requires a specific amount of fuel in the tank and also needs to have a temperature differential. As such, it can be a little tricky to get it to set.... and some areas (California included) will now allow Evap monitor not to be set.
 

HighHP

GT Owner
Jun 3, 2019
215
Spokane, WA
I don't try to keep the memory alive. I guess results here prove me wrong, but battery chargers provide dirty voltage, without being tied to a battery to stabilize. This has the potential to ruin electronics. Some electronics specifically mention...do not use with battery charger..even WHEN connected to a battery. Also, when tying a small battery into the system, bad things can inadvertanty happen. So....unless keeping the memory alive is absolutely critical, the risk of damage is very costly.
I bet "Analogdesigner" has some thoughts on this, and probably has hooked an oscilloscope to a battery charger...any comments from "analogdesigner"?
 

Specracer

GT Owner
Mark IV Lifetime
Nov 28, 2005
6,486
MA
If I have had the battery disconnected, and need to go for a state inspection, I'll simply drive it for a while. Then I scan (under $200 scan tool) it to see if monitors are "ready". If not, keep driving (the misery). Doesn't take much, really.
 
  • Like
Reactions: Stef

twobjshelbys

GT Owner
Jul 26, 2010
5,341
Las Vegas, NV
If I have had the battery disconnected, and need to go for a state inspection, I'll simply drive it for a while. Then I scan (under $200 scan tool) it to see if monitors are "ready". If not, keep driving (the misery). Doesn't take much, really.
Way less than $200. Bluetooth OBDII reader from Amazon was under $20. Free Torque app on android phone (app lists compatible readers.)
 

twobjshelbys

GT Owner
Jul 26, 2010
5,341
Las Vegas, NV
I don't try to keep the memory alive. I guess results here prove me wrong, but battery chargers provide dirty voltage, without being tied to a battery to stabilize. This has the potential to ruin electronics. Some electronics specifically mention...do not use with battery charger..even WHEN connected to a battery. Also, when tying a small battery into the system, bad things can inadvertanty happen. So....unless keeping the memory alive is absolutely critical, the risk of damage is very costly.
I bet "Analogdesigner" has some thoughts on this, and probably has hooked an oscilloscope to a battery charger...any comments from "analogdesigner"?
I'm also an "analog designer"... I would assert that most of this is "old wives tale"... The primary reason is that virtually ALL electronics are on the "other side" of the ignition switch... There are some, but very few, things that are alive when the key is off, the OBDII memory being one. And there is really no reason for that given that the info COULD be stored in flash memory...
 
  • Like
Reactions: analogdesigner

HighHP

GT Owner
Jun 3, 2019
215
Spokane, WA
Ah, good point, things that I have seen warnings on, assume the ignition is on.
 

Specracer

GT Owner
Mark IV Lifetime
Nov 28, 2005
6,486
MA
I had additional needs for my scan tool, hence the expanded budget range. Buy what you want.

Way less than $200. Bluetooth OBDII reader from Amazon was under $20. Free Torque app on android phone (app lists compatible readers.)
 

gtjoey

Keep Smiling - GT Owner
Mark IV Lifetime
Oct 14, 2005
3,414
I used the 9volt saver for My Vanquish where seats, windows, mirrors and f1 clutch relearn is saved.
There is nothing like that in the GT.
Drive it for a bit and the car recycles by itself.
Just a great car.'
MAKE SURE YOUCLEAN THE GROUND AND BOLT AND THREAD.
HIGHHP The gage comment was if the battery was flat along the way or low and surges the gages which will blow them out....
GTJOEY1314
 
  • Like
Reactions: Stef and HighHP

Indy GT

Yea, I got one...too
Mark IV Lifetime
Jan 14, 2006
2,435
Greenwood, IN
Joey, not to point out the obvious but a Ford GT is not an Aston Martin.

I would certainly rely on Kendal’s (nota4re) recommendations. He works on the GT and knows the systems.
 

dr914

GT Owner
Feb 11, 2009
179
Marietta Georgia
so battery replacement went very easily. Bought the Optima Redtop 25 at oreilly's auto parts for 91 bucks, had it in stock, put heavy blankets over the fenders, carefully removed the trunk lining, plugged in my 12 volt power source into the cigar lighter, removed the negative cable first, then the positive, rested the positive in the heavy blanket, unscrewed the battery clamp, pulled the battery up and out at an angle, pealed off the optima sticker, put a hair dryer on the ford gt battery sticker and pealed off, stuck the old sticker on the new battery and carefully reinstalled everything. Car fired up immediately with no glitches. Stuck the optima sticker on the old battery and got my 18 dollar core charge back.
Best thing is that the original battery lasted 14 years! (too bad the hood and hatch shocks do not!
 

twobjshelbys

GT Owner
Jul 26, 2010
5,341
Las Vegas, NV
so battery replacement went very easily. Bought the Optima Redtop 25 at oreilly's auto parts for 91 bucks, had it in stock, put heavy blankets over the fenders, carefully removed the trunk lining, plugged in my 12 volt power source into the cigar lighter, removed the negative cable first, then the positive, rested the positive in the heavy blanket, unscrewed the battery clamp, pulled the battery up and out at an angle, pealed off the optima sticker, put a hair dryer on the ford gt battery sticker and pealed off, stuck the old sticker on the new battery and carefully reinstalled everything. Car fired up immediately with no glitches. Stuck the optima sticker on the old battery and got my 18 dollar core charge back.
Best thing is that the original battery lasted 14 years! (too bad the hood and hatch shocks do not!
Did you verify with an OBDII reader that the adaptives were retained?