How come some use Watt-Hours and some use Ampere-Hours?
In: Technology
It depends on the power.
If you recorded a small battery in kWh then you might be advertising a battery as being 0.01kWh – which is the same as 1000mWh but sounds small in comparison.
If you had a 1kWh battery and expressed it as 1000000mWh which people would not necessarily believe the claim since it looks like an outrageous power.
With few exceptions (for example in precision engineering) you would not say that something that is 10 meters long was 10,000,000mm long, or even 10,000 cm.
When you are comparing batteries of equal voltage, using Ah or Wh are basically the same because you can just multiply by voltage. For example standard car batteries are 12V and their capacity is quoted in Ah. Why not Wh, which would work equally well? The things that a car battery powers (starter motor for example) pull a known current so it makes sense to quote capacity in current x time.
This applies to phone batteries that all work at the same voltage.
In contrast electric cars have batteries of a range of voltages. Roughly speaking higher voltage is more efficient and more compact but requires more expensive components. Hence designers pick different values depending on their needs. Given you care about the total energy stored in the battery, and you don’t necessarily know the voltage, it makes sense to quote the capacity in Wh.
Small units for small things, large units for large things.
To draw an analogy, we measure 0-60 times for cars in seconds, but the duration of World Wars in years.
Quantities for baking cakes in ounces or grams, weight of ocean liners in tons or metric tonnes.
In your example, m = milli, k=kilo. Smaller, larger.
Others have explained the difference in Ah and Wh.
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