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I think amp-hours are confusing and I wish they just gave us battery life figures in joules
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this post was submitted on 03 Apr 2026
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Why joules instead of watt hours? Also amp hours is simple to convert into watt hours. If you know the voltage then volts × amps = watts. So a 12V 100AH battery is 1200WH.
Also bear in mind that battery capacity measurements are only ever really approximate anyways because the actual capacity will vary based on how quickly you draw power from the battery. The more amps you pull the lower the capacity.
That's not strictly true, the voltage of the battery changes as it discharges, so you technically need to integrate the area under IV curve. I think Watt hours or Joules (or kilojoules or whatever makes the number a reasonable size) or anything that let's us compare across voltage would be so much better than seeing 8000 mAh 6s lifepo and you gotta know like 5 different things before you can tell
Unless you are in engineering in an energy efficient application, the estimation of Ah is good enough for 99.9% of the use case.
Yes but a fully charged battery will also have a voltage higher than its nominal voltage which mitigates that quite a bit. Also as I said in my origional comment, the rated capacity is only ever a rough measurement anyways so while volts×amphours=watthours isn't perfect, it's close enough.
I guess the part I'm missing is, when are you ever really comparing across voltage. Generally when you're shopping for batteries it's for a specific application and that application will have a specific voltage requirement. So you're only ever really going to be comparing batteries of the same voltage anyways. It isn't like you can just toss a 48V battery in something that requires a 6V battery.
Although I do agree that a voltage agnostic capacity measurement would be nice. My personal preference would be watt hours.
Battery banks are the biggest offenders to me. Like this, not only am I mad that 20 thousand mah is just 20 Ah and you gotta reduce them fractions, but it doesn't mention the battery voltage, nor do we care. Usb c outputs 5,9,12 or 18 volts but none of those are the nominal battery voltage that we would want to calculate the Wh. But since the internal voltage or chemistry is never mentioned anywhere, you can't even compare 2 different battery banks that both say 20000mAh.
It's basically just become a "bigger number better" marketing number now, and half of them are making shit up.
Wh is better for comparing two batteries.
If you are looking to buy a portable cell phone charger, they both might have the same Ah, but then you also need to know their voltage to compare. If you have the Wh, then the voltage didn't matter.
Yes but when are you comparing batteries at different voltages? If you're comparing batteries for a specific application then you're going to be looking at batteries of the same voltage.