No.ptijean32 wrote:so if I use a lead battery of 100Ah 12v, my power will be 1200 watts ....
You have a Energy 1200 Wh .
(Without going into the practical details of using a battery).
Yes, because energy = power * duration, therefore energy / power = duration, i.e. 1200 Wh / 400W = 3hptijean32 wrote:with my 400w consumer, I empty my battery in 3 hours if no additional charge?
Theoretically, yes.ptijean32 wrote:... and if I use 7 batteries of 100w in // of 12v, I will need 21h to discharge all of them? ...
And also 7 times longer to recharge them at the same charge power or 7 times more power for the same charge time.
You need an inverter suitable for the maximum power you want to use.ptijean32 wrote:in addition, I do not know if a 400w inverter exists, but it is better that I buy a higher power ... a 500w, a 750w ??? ...
To use a 400W load for several hours, a 500W inverter is suitable, a 700W will be oversized (advantage: it will age less, disadvantage: it will not be used at its maximum efficiency.)
Yes.ptijean32 wrote:using an inverter consumes energy, so do you need to plan a little more battery?
First of all, the efficiency of the inverter is not 100%, then it consumes a little while it is on (even if the load is not active).