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SteveW[_2_]

On 11/10/2012 10:15, wrote:
I've seen batteries quoted here in watt hours and amp hours. I think of a battery as a store of energy and the SI unit energy is joules. Watt hours are merely a non-SI way of expressing joules.

I know there are variables such as voltage variation and a duration of discharge and it's often best to use the unit that is less dependent on assumptions.

My impression is that phone and car batteries (for non-electric cars at least) are usually specified in amp hours.

In the weird world of domestic pv:
Which unit is more common for battery spec?
Which unit is 'better' as a guide to battery capacity?
Which unit would the sales people prefer in order to mislead you?

As we rate the power of items that run off the mains (or solar PV) in
Watts or kilo-Watts and it is useful to know how much we'll have to pay
to run them for a set time or how big an energy store we need and that
ties nicely to kWh.

SteveW