Battery & fuel consumption

[Busterboo]

Since 2016/20k miles & January 2024/80k, I've had two batteries. Each time, the fuel consumption has increased to 28.7 mpg from my normal 26.4. The first time, it slipped slowly back to 26.4 and I assume it will again now.

So what? Well, so nothing, really. I just wondered if others have had the same experience and, if so, if anyone knows why it happens?

[matsmith749]

New battery resets the charge curve from the alternator - it needs less amps to stay topped up.

Less amps = less load on the engine = better fuel efficiency.

Might be fun to run a calculator & see if it makes financial sense to change the battery every 3 years, just due to fuel savings. It might be that 2mpg over 1 year, then 1mpg for the second year saves more than the £100 to change out the battery?

It's the exact same thing when you have the aircon switched on - it uses more fuel. And the headlights too. Needing more amps from the alternator adds load, which costs fuel.

EDIT - just done the calculation. For me, doing 6k miles a year, 1mpg difference saves me £60 a year in fuel.

If I get 2mpg better for a year, then 1mpg better for a year, thats £180

So yes - changing out the battery every 3 years is a cost saving - who would have thought!

[matsmith749]

New battery resets the charge curve from the alternator - it needs less amps to stay topped up.

Less amps = less load on the engine = better fuel efficiency.

Might be fun to run a calculator & see if it makes financial sense to change the battery every 3 years, just due to fuel savings. It might be that 2mpg over 1 year, then 1mpg for the second year saves more than the £100 to change out the battery?

It's the exact same thing when you have the aircon switched on - it uses more fuel. And the headlights too. Needing more amps from the alternator adds load, which costs fuel.

EDIT - just done the calculation. For me, doing 6k miles a year, 1mpg difference saves me £60 a year in fuel.

If I get 2mpg better for a year, then 1mpg better for a year, thats £180

So yes - changing out the battery every 3 years is a cost saving - who would have thought!

Reding a bit more - is it possible that most of the mpg change is due to the adaptions etc being reset when the battery is off the car?

ie - very little real change, just the computers recalibrating etc?

[flybobbie]

Only drive with tail winds.

And what time of year did you change batteries.