Sweetsixteen
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- Jul 7, 2014
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The rate of self-discharge increases as the battery ages, so with an old battery, the alternator has to work that much harder each morning to put back what the battery has lost overnight.
Any extra load on the alternator has to be paid for in fuel.
That's obviously true, but I would be amazed if a battery made a 14 mpg difference in consumption - over 20% - because it needs a bit more work from the alternator first thing every morning.
If that were so, then working the alternator at max on a cold, damp night with lighting/aircon/heating on would crucify consumption on any car.
I have periods where I drive nights, and I have not seen huge differences in consumption from normal daytime averages.
Be interested to hear what others have found?