Watt Hour Capacity of 27 Deep Cycle battery

MrWizard wrote:
I prefer kWh listings over amp hr listings

Amphr listings are for a constant current draw, But the voltage keeps dropping
20 amps @ 12.7v is more watts than 20 amps @ 11.5v
And the draw down test goes to 10.5v
So while the amps are consistent the power used aka Watts, is not

KWH ratings give a truer rating of total power capacity

This is a puzzle worth some attention.

When using a "watt hour" meter, what are you actually measuring and how? If it uses pure amps and volts to derive the watts, then how can it be more valid than the AH meter?

If voltage is declining and amps are rising, won't the AH meter reflect the higher amps? If Watts don't care how much is amps and how much is volts to make a Watt, how can you tell if capacity is lost from the higher amps draw?

Peukert says capacity is reduced for a higher amps draw. Meanwhile Watts don't care if amps are rising since Watts stay the same if voltage correspondingly drops.

I have done load tests at the 20hr rate where it is assumed that 10 hrs is half way, but there is some confusion where things seem to go non-linear at mid- SOCs when taking SGs near 50% and the decline speeds up. (in time)

So first, if staying above 50% like good little boys and girls, then it should not matter while things are still linear, what weird things happen below 50%.

But we also see "amps creep" on the inverter's draw as voltage declines, sort of what Mr Wiz is talking about wrt constant amps but voltage declines except that the inverter tries to maintain constant Watts.

IMO using WH vs AH may be more accurate, but first there needs to be an agreement on whether the Watts measurement's input is more accurate than the AH's.

There is just something funny about those Watts thingies. :(