Thoughts on Optima batteries?

[mjonesjr84]

Northstar batteries (before they got bought out by Odyssey) did note that their batteries charged best in the 14.2 to 14.8V range. I seem to recall they even preferred the higher end of that range around 14.6V.

I set my charging voltage to 14.38V (14.4 rounds to that in HP Tuners) which is fairly typical for a modern AGM charging setpoint, at least for a single-setpoint charging voltage.

Modern cars with active BMS will generally bulk charge right at 14.4V, and then once reaching a set battery charge state (usually in the range of 75-80%) will drop as low as 13.7V depending on the accessory load. They will also ramp up to 15.2-15.3V on vehicle deceleration, which effectively charges the battery with a crude form of regenerative braking, and also serves as the de-sulfation cycle.

The TJ PCM has a battery setpoint which is adjusted based on the battery temperature sensor output. This would be fine, except that in at least some cases (like mine) where there is no battery temperature sensor, it defaults to the lowest voltage, which is right around 13.8V. Enough to basically trickle charge the battery or recover it from a very low state of charge but not enough to fully charge it in a normal cycle, and may result in early sulfation.

Interestingly, the Wranglerfix PCM had the opposite logic and charged at the maximum setpoint without the battery temperature sensor, which I seem to recall is about 14.6-14.7V.

When I adjusted the setpoints, I made it one flat curve with all values set to 14.38V since there is no battery temperature sensor in mine. With a battery temperature sensor, a milder curve than factory might be suitable for AGM.

Ideal charging voltage does in fact change with temperature (negative correlation), hence why some TJs had a battery temperature sensor in the first place. AGMs may be somewhat more resistant to overcharging than flooded cell, so setting a higher rate is less likely to damage them. Setting ~14.4V is almost always a safe bet except for the hottest of batteries.

Can you post a screenshot in HP Tuners where you changed the charge voltage? I would like to bump mine up a bit in the 2000.

 

[NashvilleTJ]

Can you post a screenshot in HP Tuners where you changed the charge voltage? I would like to bump mine up a bit in the 2000.

Here is the HP Tuners view for my Hemi, but I think the location is the same for the 4.0. Someone can check me there.

Under SYSTEM / GENERAL / Alternator: Desired Voltage:

I've been considering this change as well. I do run a battery temperature sensor, so the table should be relevant.

@Steel City 06 : Given your research here, can you suggest recommended voltages for my AGM?

 

[mjonesjr84]

Here is the HP Tuners view for my Hemi, but I think the location is the same for the 4.0. Someone can check me there.

Under SYSTEM / GENERAL / Alternator: Desired Voltage:

View attachment 645452

I've been considering this change as well. I do run a battery temperature sensor, so the table should be relevant.

@Steel City 06 : Given your research here, can you suggest recommended voltages for my AGM?

Awesome! I'll be turning off the emissions on my '00 and will make some voltage changes as well.

 

[Steel City 06]

Here is the HP Tuners view for my Hemi, but I think the location is the same for the 4.0. Someone can check me there.

Under SYSTEM / GENERAL / Alternator: Desired Voltage:

View attachment 645452

I've been considering this change as well. I do run a battery temperature sensor, so the table should be relevant.

@Steel City 06 : Given your research here, can you suggest recommended voltages for my AGM?

I would start by setting the 109°F setting to about 13.9-14.0V and then interpolating in between that and the 14.76V at 0°F setting. (Just be sure to actually measure the output after changing it to make sure it's actually doing what you think it should be doing.)

 

[NashvilleTJ]

I would start by setting the 109°F setting to about 13.9-14.0V and then interpolating in between that and the 14.76V at 0°F setting. (Just be sure to actually measure the output after changing it to make sure it's actually doing what you think it should be doing.)

Thanks mate. I also thought I'd test it before doing anything to be sure the tune is matching reality. Thanks for the temp recommendation. I do appreciate all the research you did, and information you provided, over on that other thread mentioned here. I'll be sure to post up when I make the change.



'Course, if you don't hear from me again it means my battery 'sploded from over charging, takin' me out. You will then be contacted by my aires and their technical representative - Jerry Bransford.

 

[Apparition]

Thanks mate. I also thought I'd test it before doing anything to be sure the tune is matching reality. Thanks for the temp recommendation. I do appreciate all the research you did, and information you provided, over on that other thread mentioned here. I'll be sure to post up when I make the change.



'Course, if you don't hear from me again it means my battery 'sploded from over charging, takin' me out. You will then be contacted by my aires and their technical representative - Jerry Bransford.

My dad exploded a battery in his face and was fine after they rinsed his eyes out. You can do it.

 

[KennethS]

Not having Acid and corrosion trying to get out , make an AGM even better in my rough road environment.

That was the joy of the Optimas back when they would last for many years. I had one from 2006 that lasted around 10 years in one vehicle, and one from 2018-ish that failed in 3 years in another vehicle.

 

[Link]

My dad exploded a battery in his face and was fine after they rinsed his eyes out. You can do it.

Many years ago I got battery acid in my eyes. It burned. Mom took me to the ER and they rinsed my eyes and gave me some eye drops of something. No long term issues. Can’t recommend but I did survive

 

[NDSpeed]

The Optima "Mexico manufacturing thing" was a xenophobic theory promoted by former forum member @Jerry Bransford. It has no basis in reality.

The old Die Hard Platinum Group 31 AGM batteries had the same issue with undercharging when installed as a "upsized" replacement for a factory flooded lead acid battery and charged with the vehicle alternator. The common "fix" was to periodically use a bench charger to fully charge those batteries.

The observations by @macleanflood and @NashvilleTJ suggest that there may be a similar issue with deep cycle AGM batteries such as Optima Yellow Tops and Odyssey AGM batteries when installed in a Jeep and charged with the vehicle alternator spec'd to charge flooded lead acid batteries.

An occasional full charge with a bench charger may be what is necessary to maximize the life of these AGM batteries. Since my jeep and other toys often sit for weeks between uses, it has been my practice to use a Battery Tender or other trickle charger with an appropriate charging profile to fully charge and maintain them. Those batteries have lasted 50-60% longer than the batteries that preceded them (the Varta AGM starting battery in my Sprinter has lasted 9 years so far), the only difference being my periodic use of an external charger and a battery maintainer when not in use.

YMMV

Thank you for this detailed post,

since i’ve changed to Diesel my battery is super weak, and have been contemplating buying a new deeper battery, The AGM prices have me shocked so i have t pulled the trigger yet,

in Alaska i used a trickle charger to keep the batteries from Freezing. all the vehicles have them installed. so i’ll start throwing the truck and jeep on it monthly, i did the math 328 miles last year on the Truck a 1000 on the jeep.

 

[NashvilleTJ]

OK, this is fascinating. Doing a little research on this, Google's AI gave me this information on charging voltages for AGM batteries at a given temperature:

________________________________________________________________________________________________________________________________________

Automotive AGMs are charged by the powertrain control module (PCM), which varies the voltage based on the battery's temperature
. This process, known as temperature compensation, prevents overcharging in warm conditions and undercharging in cold conditions, both of which can shorten battery lifespan.



How temperature compensation works
Lead-acid batteries, including AGMs, have a negative temperature coefficient. This means that for a given charging voltage:

• In cold temperatures, the internal resistance increases, so the voltage must be increased to ensure a full charge.
• In hot temperatures, the internal resistance decreases, so the voltage must be lowered to prevent overcharging.

The reference point for adjustment is typically 25°C (77°F). The standard compensation rate for a 12-volt battery is a reduction of -24 mV/°C (
-0.024 V/∘Cnegative 0.024 V / raised to the composed with power C
−0.024 V/∘C
) or about -13.3 mV/°F (
-0.0133 V/∘Fnegative 0.0133 V / raised to the composed with power F
−0.0133 V/∘F
).



PCM charging chart for a 12V AGM battery
The PCM uses temperature compensation to adjust the charging voltage throughout the multi-stage charging process, particularly during the absorption and float stages. The following chart provides approximate target voltages based on a typical 12V AGM absorption voltage of 14.4V at 25°C (77°F).

Temperature	Voltage adjustment for 12V system	Target absorption voltage
-20°C (-4°F)	+1.08V	15.48V
-10°C (14°F)	+0.72V	15.12V
0°C (32°F)	+0.48V	14.88V
10°C (50°F)	+0.36V	14.76V
20°C (68°F)	+0.12V	14.52V
25°C (77°F)	0.0V	14.4V
30°C (86°F)	-0.12V	14.28V
40°C (104°F)	-0.36V	14.04V
50°C (122°F)	-0.60V	13.80V

________________________________________________________________________________________________________________________________________

According to this info, for these PCM charging levels 77 degrees F is the reference point - meaning the point at which the target voltage is raised or lowered according to temperature. The values indicated are certainly more aggressive than the standard values in the PCM table on my Hemi.

From this information, I developed the following estimated voltage levels by temperature in the PCM table. The voltage for 32 degrees and 86 degrees come directly from the AI chart. The other 3 voltage levels I interpolated to get the charted line for the proposed voltages flat. The result is approximately a .5 volt increase at every temperature.

I have no idea yet if the PCM will accept these exact proposed voltages, but I may give it a try.

Does this sound reasonable? My question would be: Is the "Absorbtion Voltage" referenced in the AI information the proper target?

 

[NashvilleTJ]

Well, that was a waste of effort.... I did make the change on my rig, but rather than clog up this thread any further I posted the results over on my build thread. Here is the link if anyone is interested:

https://wranglertjforum.com/threads/nashville-tjs-build-continued.42035/post-1799506

 

[OHFIVETJ]

Odyssey in my jeep for the bad weather / hot summers & cold winters & a yellow top Optima in my 68 vette that sits 6 mo of the year hibernating. Both have great ( replacement warranties & not pro rated ) I have had many years ( optima over 10 ) of great service from both.