New battery, much better gas mileage

[Drevco]

Hi everybody there, I just want to share: the battery of my X5 4.4i/A 2004 died then I put a brand new 100Amp and the car´s simply mutated into a powerfull beast, dropping the gas toll from 20L/100km (no matter the speed) to the impressives 15,8L each 100km (running at 200km/h speed).
At 170km/h is 15,4L/100km.
In % it´s a direct 26% improvement in gas mileage
I didn´t know battery was so (SO) related to gas mileage.

[upallnight]

Your old battery may have had a dead cell(s) so the alternator was always running harder to keep it charge up.

[StephenVA]

High charging rate at the alternator (high load on the belt) causing drag on the motor. Kinda like running all the accessories at the same time during a summer down pour.

[Drevco]

that was the burned rubber smell that went away whit the old battery!!!

[srmmmm]

Change out that drive belt and be ready for an alternator replacement if it was loaded down that much.

2002 X5 3.0 306,300 miles
2014 428i 20,200 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles

1970 Firebird - under restoration

[Drevco]

Thank you for the recommendation & comments
I'm in the process (documents) to get a 2012 X5M (26.000km) actually the 4.4i/A 2004 was practically sold!
I could not make the change because of the "documentation", the car is based in a different place I live.
If belt & alternator last a little longer, it was changed just 7000km ago.. I'd tell next owner.

[oldskewel]

Glad to hear you're getting 26% better gas mileage, but it seems doubtful that just alternator load could be causing that directly.

Just some rough numbers to calculate the ~max load on the alternator:
100Amps * 14Volts = 1.4 kW, or about 2 horsepower
So this power generated by the alternator would be drawn from the engine via the accessory belt.

That seems too small to be dragging your 300+ HP ride significantly. Right?

Maybe the reduced voltage was causing some other ignition / fuel management problem that reduced MPG?

[motordavid]

^ +1...
No auto electric maven, but the OP ought to run a few tanks of his 'normal' driving and do the fill up arithmetic and compare it to pre-battery R&R.

Glancing at the instant mpg/liters per km readout on the OBC isn't exactly a real indicator of 'things are really better, mileage-wise', in my experience.
GL, mD

[white46]

If you drove highway right after battery replacement, your OBD will show much better MPG, since it's been reset as battery was removed.
Every cars suffer bad MPG from city driving, where most stop and go occurs.
But since you haven't hit city yet, it's showing highway MPG.

It's not the car actually doing better MPG.

[Drevco]

You are ALL right. I did they change in the middle of a 1900 km trip. The most impressive thing it's not the OD readings about gas mileage (which I can confirm because it 's a trip I did whith many different cars). The most impresive thing to mention is the responsiveness of the car, shifts better, accelerates better. It did said in the past error codes may one of them were about the battery but I linked with something else.