07 Accord I4 Battery Upgrade: 51R to 35

[Hall]

In all honesty, how much much juice do you need to crank over a 2.4L 4-cyl engine running 20/30wt oils? Obviously some reserve would be nice and a 35 seems like a reasonable balance.

Oh, I agree, the 35 batteries seem to work just fine. I also see more of them on shelves than 24F and the prices are often a bit lower, so I presume this comes from volume buying/selling.

My personal example is my G35 - it came with a 24F battery (and still has a 24F). Later years (technically, G37) switched to a 35. If I do a battery look-up for the battery for my car today, most selectors show it uses a 35. I want to say our son's V6 Accord used a 24F battery as well but a lot of selectors say 35.

 

[JeffKeryk]

2006 TSX 51R to 35 Part 2... I stuffed, and I do mean stuffed, the 35 into the TSX battery tray. Could not use the plastic tray and heat shield(?). I used a piece of cardboard between the battery and steel base for now. I would love to have even 1/2 inch clearance, but no luck. Pretty tight; the hold down is more for looks than functionality. Just had to bend straight the little tab.
@The Critic 's pics has me wondering if the 35 AGM is a little smaller? That would be perfect!

I will pick up a plastic tray of some kind, and the 2 gauge negative cable is coming from NAPA ($16).

 

[The Critic]

Later years (technically, G37) switched to a 35.

Actually, the 35's rarely last more than a year or two in the G37's. There was actually a TSB on the early models recommending an "upgrade" to a 24F:

https://infinitig37.com/TSB/1ST34.pdf

We usually installed the 24F's on all G37's as an upgrade.

 

[The Critic]

2006 TSX 51R to 35 Part 2... I stuffed, and I do mean stuffed, the 35 into the TSX battery tray. Could not use the plastic tray and heat shield(?). I used a piece of cardboard between the battery and steel base for now. I would love to have even 1/2 inch clearance, but no luck. Pretty tight; the hold down is more for looks than functionality. Just had to bend straight the little tab.
@The Critic 's pics has me wondering if the 35 AGM is a little smaller? That would be perfect!

I will pick up a plastic tray of some kind, and the 2 gauge negative cable is coming from NAPA ($16).

Might need to order the V6 battery tray and see if it fits in that spot.

 

[The Critic]

Why? The alternator only needs to put back into the battery what has been taken out. Barring something like a completely dead battery that was jump-started, or a faulty battery with a shorted cell, a larger battery would not be expected to require any more out of an alternator than a smaller one.

EDIT: From what I've observed there isn't much correlation between the alternator size and the battery capacity. Alternator size is based on presence of things like electric cooling fans, and battery size is based on engine displacement.

Most Euro cars require for the battery size to be coded to the vehicle by aH rating. Supposedly charging output is dependent on this.

 

[brianl703]

Most Euro cars require for the battery size to be coded to the vehicle by aH rating. Supposedly charging output is dependent on this.

Outside of that, have you ever seen any charger designed for lead-acid batteries that wanted to know how many AH the battery being charged is?

I haven't.

I suspect the reason Euro cars want to know how many AH the battery is is so they can detect a battery that is getting weak or is faulty.

 

[carviewsonic]

I went for the extra CCA's and installed a 24F in my '07 Accord. Forecast is for several days of -30C temps starting this Sunday, so extra CCA's are nice to have. It's a bit tight, but I'm satisfied with the clearances and access to the transmission dipstick.
A group 35 would have been adequate however, with a bit less weight and a few less dollars.

Amazingly, I somehow got 10 years from the original OEM 51R battery, then 7 years from the replacement 51R (I did regularly use a maintenance charger since I had little confidence in the small battery).
Cranking in really cold temps was very slow. Fortunate that my wife (who drove it to work for years) never needed a boost. It cranks fast now in cold weather with the 24F, much more confidence inspiring.

From the web:

Dimensions​

With these two batteries, the difference in size is relatively minute. Group 24F batteries measure 10.3 x 6.8 x 8.9, whereas the Group 35 batteries measure 9.1 x 6.9 x 8.9.
Immediately you can see that the 24F battery is that bit longer than the Group 35 battery. The 24F weighs about 4 lbs more.

 

[Hall]

Actually, the 35's rarely last more than a year or two in the G37's. There was actually a TSB on the early models recommending an "upgrade" to a 24F:

We usually installed the 24F's on all G37's as an upgrade.

That's kinda funny.... Just checked again and for '08 models, selectors still say a 35 fits. Check an '09 and '12 and also say to use a 35. I guess the battery people didn't get the Nissan memo. That bulletin is specific the coupe models too. Wonder why not for sedans.

I noticed they say to replace an EVAP valve too. How is it related ?

Most Euro cars require for the battery size to be coded to the vehicle by aH rating. Supposedly charging output is dependent on this.

I suspect the reason Euro cars want to know how many AH the battery is is so they can detect a battery that is getting weak or is faulty.

My wife's Fusion (I know it applies to many other Ford models as well) has multiple options / selections for the BMS (Battery Management System) regarding batteries. Anytime a battery is replaced, you really should "reset" the BMS and if a different battery goes in, you tell it some specs. Some of the choices are AGM/70Ah/600CCA, AGM/80Ah/700CCA, Standard/60Ah/600CCA, Standard/90Ah/800CCA, and more.

 

[carviewsonic]

That's kinda funny.... Just checked again and for '08 models, selectors still say a 35 fits. Check an '09 and '12 and also say to use a 35. I guess the battery people didn't get the Nissan memo. That bulletin is specific the coupe models too. Wonder why not for sedans.

I noticed they say to replace an EVAP valve too. How is it related ?



My wife's Fusion (I know it applies to many other Ford models as well) has multiple options / selections for the BMS (Battery Management System) regarding batteries. Anytime a battery is replaced, you really should "reset" the BMS and if a different battery goes in, you tell it some specs. Some of the choices are AGM/70Ah/600CCA, AGM/80Ah/700CCA, Standard/60Ah/600CCA, Standard/90Ah/800CCA, and more.

I wonder what Ford is optimizing here, battery life or a teensy gain in mpg by not always fully charging the battery? Can you access the BMS menu easily, or is a scan tool required?

Edited to add - Did a quick search, the BMS seems to mostly be a feature related to stop/start systems.

 

[brianl703]

My wife's Fusion (I know it applies to many other Ford models as well) has multiple options / selections for the BMS (Battery Management System) regarding batteries. Anytime a battery is replaced, you really should "reset" the BMS and if a different battery goes in, you tell it some specs. Some of the choices are AGM/70Ah/600CCA, AGM/80Ah/700CCA, Standard/60Ah/600CCA, Standard/90Ah/800CCA, and more.

AGM batteries like a different charging voltage than standard batteries.

Putting a larger battery (in AH) than what the system thinks is in there isn't going to harm the alternator.

 

[Hall]

I wonder what Ford is optimizing here, battery life or a teensy gain in mpg by not always fully charging the battery? Can you access the BMS menu easily, or is a scan tool required?

One reason for it is definitely MPG. I think what I read is they literally shut off the alternator when possible. No idea how they do it though.... There's no clutch on the pulley, to my knowledge, so maybe they can de-energize the windings/magnets which removes any "drag" on the belt pulley ???

You access it with a scan tool. I replaced the battery (Group 90, as I recall) with an H6 AGM so I told the BMS the specs for this new, bigger battery, and also reset it. Used FORScan to do this. I bought an INNOVA scan tool recently but haven't connected it to her car to see what I can do, if anything, related to this.

 

[carviewsonic]

One reason for it is definitely MPG. I think what I read is they literally shut off the alternator when possible. No idea how they do it though.... There's no clutch on the pulley, to my knowledge, so maybe they can de-energize the windings/magnets which removes any "drag" on the belt pulley ???

You access it with a scan tool. I replaced the battery (Group 90, as I recall) with an H6 AGM so I told the BMS the specs for this new, bigger battery, and also reset it. Used FORScan to do this. I bought an INNOVA scan tool recently but haven't connected it to her car to see what I can do, if anything, related to this.

I'm wondering if that negatively affects battery life? Hopefully not, but when it comes to squeaking out an extra fraction of a mpg...
Depends on how the system is programmed I suppose.

 

[brianl703]

One reason for it is definitely MPG. I think what I read is they literally shut off the alternator when possible. No idea how they do it though.... There's no clutch on the pulley, to my knowledge, so maybe they can de-energize the windings/magnets which removes any "drag" on the belt pulley ???

They can turn off the field coil.

I considered doing something like that on an old car. Put a deep-cycle marine battery in it, add a switch to turn off the field coil on the alternator, and charge it up when I got home.

Wonder how many MPG that would actually gain.

 

[bbhero]

After reading @carviewsonic’s thread and receiving some encouragement from @bbhero, I decided to upgrade the battery in my wife’s Accord from a 51R to a 35.

I ordered the battery tray, battery cover, larger ground cable, new tie-down, both J-Hooks and both nuts from Honda for $128.43.

For the battery, I used a Kirkland 35 AGM, which was $179.99.

Everything fits securely, but it is tight. I think the V6’s wiring harness and air box are slightly different in this area.

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Great job my friend... You have way, way, way more the enough talent and ability to make this upgrade. Granted you do live in a very mild climate... If you were to take that car up in the mountains and farther Eastward into say Utah or Colorado... That extra CCA and reserve capacity is a nice buffer to have in place. If the alternator were ever to give out... The extra reserve capacity would be more with a AGM group 35 vs a 151r. Even 10-20 minutes more can easily make a big difference.

If you lived meat me 2 things would be guaranteed to happen...

1. I would have you and yours over for dinner and smoke a rack of beef ribs or pork ribs or spiral ham....

2. I would like to go by your place and give you a extra pairs of hands.... Also bringing my portable charcoal grill and smoke hotdogs while you were working...

 

[JeffKeryk]

Great job my friend... You have way, way, way more the enough talent and ability to make this upgrade. Granted you do live in a very mild climate... If you were to take that car up in the mountains and farther Eastward into say Utah or Colorado... That extra CCA and reserve capacity is a nice buffer to have in place. If the alternator were ever to give out... The extra reserve capacity would be more with a AGM group 35 vs a 151r. Even 10-20 minutes more can easily make a big difference.

If you lived meat me 2 things would be guaranteed to happen...

1. I would have you and yours over for dinner and smoke a rack of beef ribs or pork ribs or spiral ham....

2. I would like to go by your place and give you a extra pairs of hands.... Also bringing my portable charcoal grill and smoke hotdogs while you were working...

@The Critic is a good guy; always willing to share his sound advice and time. He live about an hour away in a nice part of town.

 

[Hall]

I'm wondering if that negatively affects battery life?

I definitely don't want to jinx anything but I just checked and I installed the current battery (an H6 AGM from AAP, pre-Diehard switchover) in Nov 2017. I do put it on my smart/trickle charger 1-2 times a year.

 

[carviewsonic]

delete

 

[ctechbob]

I wonder what Ford is optimizing here, battery life or a teensy gain in mpg by not always fully charging the battery? Can you access the BMS menu easily, or is a scan tool required?

Edited to add - Did a quick search, the BMS seems to mostly be a feature related to stop/start systems.

They're optimizing for MPG. BMS is only set to charge to 80% in my Ranger, and yes it looks like it is hard on batteries. They come with an AGM which should go 4-5 years, but the guys with the 2019's are replacing theirs left and right.

I'm on battery #2 already in my 2020 and it was a pre-virus truck. Whether Ford got a bad batch of batteries or not, it seems like it is just an issue waiting in the wings. As soon as my kid's Jeep gets fixed and I get my truck back from the wife, I'm resetting my BMS to charge to 90%. I already have my AutoStopStart disabled.

And yes, you need something like Forscan to re-write the table in the ECU to change it.

 

[carviewsonic]

After reading @carviewsonic’s thread and receiving some encouragement from @bbhero, I decided to upgrade the battery in my wife’s Accord from a 51R to a 35.

I ordered the battery tray, battery cover, larger ground cable, new tie-down, both J-Hooks and both nuts from Honda for $128.43.

For the battery, I used a Kirkland 35 AGM, which was $179.99.

Everything fits securely, but it is tight. I think the V6’s wiring harness and air box are slightly different in this area.

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Looks factory correct, a tidy installation. At cold temps the improvement in cranking speed will be noticeable.

 

[carviewsonic]

They're optimizing for MPG. BMS is only set to charge to 80% in my Ranger, and yes it looks like it is hard on batteries. They come with an AGM which should go 4-5 years, but the guys with the 2019's are replacing theirs left and right.

I'm on battery #2 already in my 2020 and it was a pre-virus truck. Whether Ford got abad batch of batteries or not, it seems like it is just an issue waiting in the wings. As soon as my kid's Jeep gets fixed and I get my truck back from the wife, I'm resetting my BMS to charge to 90%. I already have my AutoStopStart disabled.

And yes, you need something like Forscan to re-write the table in the ECU to change it.

Batteries are expensive, I doubt owners would ever recoup the additional battery replacement cost with fuel savings. I actually don't know how much an alternator charging from 80% to 100% affects fuel economy, but it seems to be a poor strategy from the vehicle owner's perspective.
I know, trying to meet CAFE requirements, but still.