Replaced my Die hard AGM now MPG went up

[LenZee]

Bought old battery 6/23/15 and been testing it every few months with a cheap amazon battery tester. It is still usable but CCA is testing at 485 for a 710 CCA battery.
Still cranks fast but wanted to change it out before it got too low. Last week I bought a replacement from Walmart (EverStart Platinum AGM) and then reset the MPG counter and now I'm easily getting 2 mpg+ driving my usual routes. Went from 17.8 to 20.3 with no difference in driving . I guess the alternator may have been pulling down the gas mileage. New battery tests at 820cca and is rated 710cca.

 

[LenZee]

I just realized I replaced my wife's same AGM a few months ago, Now I need to check her MPG. Her battery was a year younger but tested low and cranked real slow in the cold.

 

[Trav]

I would put it down more to ECM relearn.

 

[LenZee]

I would put it down more to ECM relearn.

No ECM relearn, battery backup was used to preserve my radio stations.

 

[nwjones18]

Personally I don't trust any MPG figure that wasn't done on a calculator at the pump.. None of the ones on my cars are ever exactly right and on my truck I have one that hasn't been reset in 20k miles... It skews to what the latest mpg's are not the 20k average.. I think this may be an example that correlation does not imply causation, but who know it may be lugging the alternator a little less.

 

[Pelican]

Bought old battery 6/23/15 and been testing it every few months with a cheap amazon battery tester. It is still usable but CCA is testing at 485 for a 710 CCA battery.
Still cranks fast but wanted to change it out before it got too low. Last week I bought a replacement from Walmart (EverStart Platinum AGM) and then reset the MPG counter and now I'm easily getting 2 mpg+ driving my usual routes. Went from 17.8 to 20.3 with no difference in driving . I guess the alternator may have been pulling down the gas mileage. New battery tests at 820cca and is rated 710cca.

I see no reason how/why a battery would affect MPG, other than perhaps the electronic mpg counter was not working right with the old one.

 

[LenZee]

I see no reason how/why a battery would affect MPG, other than perhaps the electronic mpg counter was not working right with the old one.

If the alternator was working harder that could be the drag on mpg. I usually reset the mpg counter every 2 to 3 months and in 2015 when I bought it, It got 21mpg and over the years settled to the 17.8 eventually until the battery was replaced. Tune up was done a year ago so plugs are fresh.

 

[f355spider]

I see no reason how/why a battery would affect MPG, other than perhaps the electronic mpg counter was not working right with the old one.

Alternator operation affects MPG, that is why many newer cars like BMWs have "intelligent battery sensor" systems that adjust the output of the alternator based on battery age and condition. This allows the alternator to not work as hard, when not needed...all to improve mpg.

I am unsure if a big a difference is accountable for the OPs mileage improvement, but car manufacturers have identified that alternator loads on the engine are worth considering

 

[kschachn]

To achieve this sort of MPG differential that old alternator must have been on fire.

 

[Hall]

If the alternator was working harder

Not sure that alternators work harder. On newer cars, the alternator can "turn off" when not needed but not sure if either your vehicles have this ability.

 

[Rand]

it would be less than 1 mpg.

 

[Lubener]

I don't buy into it.

 

[Nesterenko]

Not sure that alternators work harder. On newer cars, the alternator can "turn off" when not needed but not sure if either your vehicles have this ability.

He has a '12 Sienna, I've got a '12 Yaris. Mine seems to operate as such according to the Ultra gauge I have hooked up. Maybe his alternator does compensate for electrical load.

 

[Astro14]

If the alternator was working harder that could be the drag on mpg. I usually reset the mpg counter every 2 to 3 months and in 2015 when I bought it, It got 21mpg and over the years settled to the 17.8 eventually until the battery was replaced. Tune up was done a year ago so plugs are fresh.

2 MPG?

Not that much drag - the math doesn’t work…

 

[LenZee]

If the alternator was working harder that could be the drag on mpg. I usually reset the mpg counter every 2 to 3 months and in 2015 when I bought it, It got 21mpg and over the years settled to the 17.8 eventually until the battery was replaced.

2 MPG?

Not that much drag - the math doesn’t work…

I'll update in a week and see where it goes, Nothing else has changed.

 

[kschachn]

I'll update in a week and see where it goes, Nothing else has changed.

Oh there are many things that have likely changed. In fact I'll guarantee it.

 

[RaymondP]

Changed out the factory AGM battery on a Mercedes E350 4Matic after eight years, even though a battery test indicated all good. Was getting a number of strange anomalies I couldn't resolve or identify cause. New AGM battery correctly commissioned and installed, and all issues went away with car running smoothly. Can't comment on milage change but noticeable improvement in operation.

Similar issues with motorcycle. Borderline tested OK, but new battery provided a much better running ride. Finding with newer vehicles a "PASS" on a battery test doesn't always mean a hold on the replace if they are approaching the end of their life. Seems they appreciate the extra output of a less aged battery. For info. these have all been AGM batteries.

 

[4WD]

2 MPG?

Not that much drag - the math doesn’t work…

He left off the 0.

 

[LenZee]

Just an update, MPG settled on 20.4 after the second tank of gas. My wife's car did not change after her battery was replaced.
I'll post an update in another month.

 

[brianl703]

I am unsure if a big a difference is accountable for the OPs mileage improvement, but car manufacturers have identified that alternator loads on the engine are worth considering

If the OP's battery were pulling enough current to cause a 2MPG difference, it would be smoking, steaming, or on fire.