Watt Hrs vs Amp Hrs
This article helps explain these ratings and raises a question wrt battery charging older vs newer LFPs too. Not sure if this also applies to other battery types or if it matters with any when you me...
Forum Discussion
For rough operation in Wh, you can simply multiply Ah by the nominal voltage of the battery (as opposed to whatever its current voltage is), assuming one is working with a single voltage and a single battery.
For accurately measuring energy usage, you'd integrate the instantaneous product of voltage and current over time--which is basically what an electric meter does. Of course, with AC power, phase relationships and power factors must also be considered; but for a DC meter, there are no phase relationships to worry about.
To determine the state of charge of a battery, simply integrating net charge or net power is too naïve to be useful, since the response of a battery is hardly linear thanks to the Peukert effect, among other things. To figure that reasonably accurately requires more complex math. I suspect in the majority of cases, determining the state of charge is really the goal, rather than just how many amp-hours or watt-hours have gone into or out of the battery.
For accurately measuring energy usage, you'd integrate the instantaneous product of voltage and current over time--which is basically what an electric meter does. Of course, with AC power, phase relationships and power factors must also be considered; but for a DC meter, there are no phase relationships to worry about.
To determine the state of charge of a battery, simply integrating net charge or net power is too naïve to be useful, since the response of a battery is hardly linear thanks to the Peukert effect, among other things. To figure that reasonably accurately requires more complex math. I suspect in the majority of cases, determining the state of charge is really the goal, rather than just how many amp-hours or watt-hours have gone into or out of the battery.
