Well, load shedding is supposed to be 2 hours, up to 4 times a day, with at least 2 hours between each cycle. however there is a very good chance that, due to the massive cooling load that is connected, the switching circuitry will experience either a massive prolonged overcurrent event on reconnection, or the switchgear will fail and not connect. This then results in prolonged outages, and as Pieter is down the coast, and at the end of single power lines with little to no redundancy on the 132kV supply side, and limited MV supplies as well, with often the supply side fuses blowing ( explosively, see Rodalco and Big Clive for video) and disconnecting whole loops, and then secondary LV side 400A fuses suffering from repeated pulse loads and dropping phases randomly.
There are a few UPS suppliers around, Tower is quite reasonable, and South African supported, but you will pay R8k for an extra battery box, and R12k again for all those Deltec batteries to fill it with the 72 needed. Will do at least 8 hours with the default battery set if you fill the other bank in the cabinet, with the 36 required, at your load. Stay away from the mystery brand ones, and Makro online has a range of UPS options available, with store collect ( and a forklift or crane truck for the bigger ones) along with Takealot, though your courier will be saying " Hau Baas, Aikona!" when delivering them if you expect to door delivery.
Buying extra battery packs for the rack will work, and in general there are very few UPS units that are happy with generator supplied power anyway, unless you have a giant big diesel 15kVA unit, with both frequency control and voltage regulation, such that the voltage is within 10% and frequency is within 1%. Most smaller units will not do this, and the wide frequency range option is often only available on certain models, some are incredibly fussy.
I have an APC UPS at home, just had to replace the 2 19Ah SLA batteries, as they were so dead that they would not charge with 70V applied from the welder. Instead of getting 2 new 19Ah batteries, I instead went and bought 2 636 deep cycle batteries, and used the internal battery bay to install a massive 15000uF 63V computer grade electrolytic with screw terminals. Then used the Anderson plug on the rear to connect the 2 deep cycle batteries in series. Now will do 2 hours after doing the recalibrate, and thanks to there being USB, and Linux having reasonable APC support built in, I am able to survive load shedding.
Eaton is a lot better, and while I have a (used) Eaton 3kVA unit around, I am loath to go buy 4 deep cycle batteries to use it, as it is 48V powered. Another APC is 36V, same reason, batteries cost money, and I got the UPS units free as they had dead batteries. $100 per battery is not cheap, even more so if I go for the top range of batteries, at near $200 each. Even the correct 15 minute internal batteries are $80 each.
As to generators, you cannot buy a generator at the moment, all on back order, because of the Prince of Darkness having insufficient available capacity to handle the load, and not having working power plants for various reasons, and also because the HVDC poer line form Moz being slightly faulty, due to having had a tropical storm run through. In the USA that would be Katrina type of disaster, but here it is just summer. Also there is a shortage of candles.
But, going to cut this short, as I am also suffering internet shedding, so am using mobile data to connect. thank you for unlocked Android phones, so you do not need to beg the mobile network supplier to allow tethering on the carrier locked phones.