Sponsored

Battery / Trickle Charging / Increased MPG?

xeon

Well-Known Member
First Name
John
Joined
Jan 18, 2018
Threads
13
Messages
332
Reaction score
250
Location
California
Vehicle(s)
JLU Rubicon
I have a 2018 JLUR and have replaced the main and aux battery three times so far. I just crossed 60,000 miles. During the first few years of ownership, I used it to commute to work but now I am lucky to put 3000 miles on it a year. So it sits in the garage a lot waiting for its next adventure. During the past year, I started to notice that my alternate would be maxing out during every drive (pegged at 14.5V) as it tried to charge the batteries. My MPG in the city was nothing unusual 15.5 to 16 MPG city, 19 to 20 MPG highway. The annoying thought of having to replace the batteries again made me pull the plug and purchase a Noco10 and then a Noco5. Both work great...the 5 is just that much easier to mount and I don't need the speed of the 10 since my JLUR sits so long.

After letting the battery get a complete charge things with the Jeep started working differently. I noticed the alternator did not fully engage during any of my short trips. Instead of the full load of 14.5+ I would see trickles at 12.5 to 12.7. I didn't think much of it other than the battery is charged and all is good.

However, in longer trips 100 miles plus on the highway I noticed something very different. Where I normally get 19 to 20 MPG (35" K02s at 34 psi, automatic trans, cruising between 65 and 75) I am now getting between 24 and 26 mpg. Why the big jump? Of course, I was skeptical. Maybe it was the truck I was behind for a long time on that first time out.

After a few tests. I am consistently between 24 and 26 mpg on the highway when the battery has been fully charged and the alternator does not seem to be doing much of anything. If I do not charge the jeep and take it out...the alternator is constantly charging the battery pumping out 13.3 to 14.5 volts and when this occurs I am getting the typical 19 to 20 MPG.

I honestly can't figure out why the big difference. I am guessing it's the alternator drag. I am hoping others here that use a battery maintainer can chime in and let me know what they are experiencing. Maybe my alternator is just a "drag" and it needs to be replaced. Not sure. Any other thoughts on this would be greatly appreciated. For the next few tests, I am going to assume the onboard computer that is calculating the MPG is drastically off. I use it more as a gauge of normalcy vs accuracy but now I have to question that too.

IMG_1329.jpg
Sponsored

 

jeepdabest

Well-Known Member
First Name
Bobby
Joined
Mar 27, 2019
Threads
20
Messages
980
Reaction score
1,548
Location
Arizona
Vehicle(s)
2019 JL Sahara
Alternator drag won't affect mileage that much.
 

Fudster

Banned
Banned
Banned
First Name
Elliot
Joined
Mar 9, 2022
Threads
29
Messages
657
Reaction score
673
Location
Athens, GA
Vehicle(s)
2019 Sahara
I have a 2018 JLUR and have replaced the main and aux battery three times so far. I just crossed 60,000 miles. During the first few years of ownership, I used it to commute to work but now I am lucky to put 3000 miles on it a year. So it sits in the garage a lot waiting for its next adventure. During the past year, I started to notice that my alternate would be maxing out during every drive (pegged at 14.5V) as it tried to charge the batteries. My MPG in the city was nothing unusual 15.5 to 16 MPG city, 19 to 20 MPG highway. The annoying thought of having to replace the batteries again made me pull the plug and purchase a Noco10 and then a Noco5. Both work great...the 5 is just that much easier to mount and I don't need the speed of the 10 since my JLUR sits so long.

After letting the battery get a complete charge things with the Jeep started working differently. I noticed the alternator did not fully engage during any of my short trips. Instead of the full load of 14.5+ I would see trickles at 12.5 to 12.7. I didn't think much of it other than the battery is charged and all is good.

However, in longer trips 100 miles plus on the highway I noticed something very different. Where I normally get 19 to 20 MPG (35" K02s at 34 psi, automatic trans, cruising between 65 and 75) I am now getting between 24 and 26 mpg. Why the big jump? Of course, I was skeptical. Maybe it was the truck I was behind for a long time on that first time out.

After a few tests. I am consistently between 24 and 26 mpg on the highway when the battery has been fully charged and the alternator does not seem to be doing much of anything. If I do not charge the jeep and take it out...the alternator is constantly charging the battery pumping out 13.3 to 14.5 volts and when this occurs I am getting the typical 19 to 20 MPG.

I honestly can't figure out why the big difference. I am guessing it's the alternator drag. I am hoping others here that use a battery maintainer can chime in and let me know what they are experiencing. Maybe my alternator is just a "drag" and it needs to be replaced. Not sure. Any other thoughts on this would be greatly appreciated. For the next few tests, I am going to assume the onboard computer that is calculating the MPG is drastically off. I use it more as a gauge of normalcy vs accuracy but now I have to question that too.

IMG_1329.jpg
given the smart alternator taxing the engine less when the batteries need less of a charge, I imagine to a small extent you can trade off charging your batteries with the shore power of trickle charging (or some onboard solar setup) rather than with liquid fuel, but those mileage improvements are not my experience despite also regularly having my jl on a trickle charger at rest.

even the additional ESS events that charged batteries might allow I’d think can’t explain your improvements, but good for you if they’re genuine!

are you running with high current drawing aftermarket appliances…?
 

Vinman

Well-Known Member
First Name
Vince
Joined
Oct 19, 2020
Threads
28
Messages
1,024
Reaction score
2,534
Location
Calgary, Alberta
Vehicle(s)
2021 JLU Rubicon
Having the battery topped up by trickle charging could have an impact on fuel economy.

Side story. My brother used to have a late 70’s Pontiac Trans-Am he raced.
Built 455 auto. He swore up and down that when he disconnected the alternator prior to a pass he would consistently run almost 1/10 of a second faster than with the alternator connected.
That car would have had a 100 amp alternator at best, the Jeeps are over double that so I can certainly see much more drag produced by our alternators which in turn would negatively impact fuel economy.
 
OP
OP
xeon

xeon

Well-Known Member
First Name
John
Joined
Jan 18, 2018
Threads
13
Messages
332
Reaction score
250
Location
California
Vehicle(s)
JLU Rubicon
Update:
Had a chance to make another 120 mile trek on the freeways today. The battery was fully charged, tank full...and eagerly awaited the results. After the trek...the dash reported 25.4 MPG. After fill up, it seemed it was actually a bit better coming in at 25.6. Both methods are pretty gross and have limited accuracy but what I can say is there is a remarkable improvement from the typical 19-20 mpg that I would normally see.

Its the holidays in SoCal so the freeways are light in the morning but not nearly as heavy as they would be during a typical work week so this could be a factor. But I have never seen my Jeep report that I was getting such high MPG. At one point today I was at 27.3..WTF while on the freeway...it didn't drop until I had to get off at my destination and drive a few city miles.

Well I am just going to enjoy the savings and keep monitoring but if any other jeepers get a chance to test this out with me....let me know how it goes.
Sponsored

 
 



Top