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What is the capacity in Wh of a 3000mAh Lion battery?

Volt x Amp isn’t the answer I think because the safe voltage of a cell ranges between 2.5 and 4.2.

When a manufacturer states 3000mAh is that between the safe range? Or when totally depleted and damaged, just to be able to advertise a high number?

I’m aware that 3000mAh also depends on how many amps you pull, but even then can a cell deliver say 2A if it gets close to 2.5v, even if it’s spec states 10A continuous?

Is there some rule of thumb to calculate the real world Wh?

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You don’t calculate the energy, you measure it. But often multiplying the electric charge (Ah) with the nominal voltage (usually defined as 3.6 or 3.7V) gives you a good approximation.

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P (power in Watts) = I (current in Amps) × V (voltage). In most cases, it’s interchangeable whether capacity or applied power.

For a 3400mAh lithium Ion cell, with a NOMINAL voltage of 3.7V
P(Wh)=I(Ah) × V, so
P = 3.4×3.7=12.58 Wh.

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As Henk stated, you have to measure it at whatever specific draw level you expect to be operating at. If the cell states “up to continuous 10A discharge”, then it will sustain up to 10A discharge continuously, thus maintaining that capacity. Most of the time though, that’s the rating of a protection circuit, for the longevity and safety of the cell/battery in question.

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All clear.
The expected draw is under 0.8A
I guess that’s so low for a 21700 that V*A is pretty close to real life.

Thanks .

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