Calculating UPS Backup Time for 600VA 360W Model with 0.55 Efficiency Factor

Hello,

as in the topic, I am asking for help in finding out in my calculations regarding the calculation of the time for which the UPS will support the device.

It is a 600VA 360W UPS. So far, I have been able to locate 2 patterns:

I want to calculate the backup time and I used the formulas where:
QA - battery capacity [Ah]
UA - battery voltage [V]
P - power of the powered device [W]
0.55 - a factor that takes into account the efficiency of the UPS, battery discharge and the nature of the receiver


Example:
P = 100 W - power consumed by the connected device
UA = 12 V - voltage of the battery connected to the UPS
QA = 7 Ah - capacity of the battery connected to the UPS


Backup time:
t = (coefficient * (QA * UA)) / P = time result ---- the result is: 27.72 minutes (this is the formula I deduced after looking at the electrode)

While searching the internet, I found a pattern like this:
t = Factor * ((402 * (P / 12) ^ (- 1,3)) / 7) * QA = time result ----- the result is: 14.05 minutes (this formula is a mystery to me - something is counting, but I don't know what and how)

I am asking for help and for guidance, because my hands have already dropped to the ground.

Regards,
Mariusz

The first formula is a correct calculation for peasant reason.
100 W / 12 V = 8.3333 Ah per hour
8.333333 / 60min = 0.1388889 Ah per minute
7 Ah / 0.1388889 = 50.39996 this is 50 minutes and 24 seconds
50.39996 x 0.55 = 27.719978 that is 27 minutes and 43 seconds

I will step on, because there are a million topics, and this topic fits.
I have a power supply as in the link http://www.salicru.com/files/documentacion/ficha-pdf-5641aa34cb4df ingles.pdf
With the following information: (Typical back up time (3) - 10 minutes, (3) At 75% of load), can I calculate the backup time for loads of 30%, 50%, 100%?