Yes i did mean 3 to 400 watts per hour.

No!, You were right first time. It is important to understand the difference.

A WATT or a KILOWATT is a measure of POWER.

A WATT HOUR or a KILOWATT HOUR is a measure of ENERGY.

ENERGY and POWER are two different things. ENERGY = POWER * TIME.

If you are stating POWER then you are correct with 3-400 WATTS or if you are stating ENERGY then you should be using WATT HOURS or KILOWATT hours.

There is a massive difference between the battery requirements to support a load of 3-400 WATTS for say 12 hours, than if you are stating that you only use 3-400 WATT HOURS in total over night. 3-400 WATTS * 12 HOURS = 3,600 to 4,800 WATT HOURS or 3.6 to 4.8 KILOWATT HOURS if you prefer.

400 WATT HOURS = 33 AMP HOURS @ 12 VOLTS.

4.8 KILOWATT HOURS = 400 AMP HOURS @ 12 VOLTS.