Cor van de Water wrote:

> Reason is that Li-Ion batteries are sized by Ah
> so it is normal to say what size (Ah) battery cells you have,
> if you want to indicate which version cells are in your pack,
> but if you want to tell the energy in the pack then it only
> makes sense if you tell (or know) the average pack voltage to
> arrive at the kWh rating from Ah * Volts, or simply talk about kWh.

In fairness, *all* batteries are sized by Ah, so I think this reason applies 
equally regardless of the battery chemistry.

I think the reason for talking/writing in terms of Ah rather than Wh depends 
somewhat upon the context.  When buying a battery for an EV, we seldom buy a 
single battery of the entire pack voltage; instead we buy some number of 
discrete modules from which we assemble a battery that suits our specific (and 
often arbitrary) overall voltage and capacity need.  These modules may be 
individual cells (typically the case for lithium), or they may be monoblocs 
consisting of multiple cells (usually 3, 4, or 6 for PbA) in a single case.  
Either way, the individual modules are rated in terms of Ah capacity (at a 
specific discharge rate for PbA), so it is not uncommon to talk in terms of Ah 
when discussing options as the nominal voltage of the module being considered 
is often implied by the chemistry or application.

The other scenario that comes to mind is when people discuss how much energy 
their EV consumes in use, and in this case I suspect the reason Ah would be 
used instead of Wh or kWh is due to the limitations of the instrumentation 
available.  The only meaningful value is the energy consumption in [k]Wh, 
whether from the battery or outlet, however, if one has only has a gauge 
capable of reporting energy usage in Ah (or only uses the Ah display of a more 
capable meter because their primary interest is in 'fuel gauging' rather than 
energy usage), then this is the value they will offer to quantify their energy 
usage.

Cheers,

Roger.

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