Eon

At the end of 2020 I bought a 3000W 24V Growatt inverter and paired it with 2X 200Ah Allgrand batteries just to use as a load shedding cure. According to the initial calculations, I would've been able to get +- 9 hours out of this system while using about 200 - 250W. The formula according to the inverter salesperson was as follows: 1) Take the Ah of the batteries and multiply it by the system voltage to get the total Watt hour, so 200Ah X 24V = 4800W/hour. 2) Take the total W/hour and multiply it by the desired battery Dod percentage, so 4800 X 50% = 2400 usable W/hour. 3) Then devide the usable W/hour by the load to het the backup time. 2400/250W = 9.6 hours. The 250W is made up of my fridge, TV, router and phone charger. Is this calculation correct? In my tests I've only been getting about an hour and a half before the low voltage cut off (24V) is reached. So either my inverter/battery settings are way off, my batteries are damaged, or I've been fed a fart by the salesperson. Any help would be great. Thanks.