Quote:
Originally Posted by mpg_numbers_guy
Are you saying your new (lithum?) battery improved your fuel economy over a standard 12V battery? By how much?
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Hard to say exactly since there are so many variables.
-The 12v was probably getting weak weeks or months before and thus causing my charger to draw more power from the engine.
-Charging a lithium battery is more efficient than a lead acid, and charging capacitors is a lot more efficient than that, even.
However I'd say that's largely irrelevant because the lithium battery is behind a resistor so it's not playing much of a role here, it's mostly just keeping the caps topped off when the car is off. You're mostly seeing supercapacitors vs a lead acid battery (which in this dataset declined very rapidly as temperature dropped).
From what I understand a 12v battery will have a resting voltage of around 12.6v. While your car is running, your alternator (or DC-DC converter) is producing a higher voltage than that. This causes current to trickle into the battery, which is turned into heat and lost while the battery is full. By contrast, a lithium battery OR supercapacitors will actually sit at that ~14v the charging system provides. Maybe someone with a better electrical background can provide more or better information.