Product quality sucks!

I bought a RCT Megapower inverter in June 2023 from BWH Erasmus Park in Pretoria. At first, I was very impressed with the performance as it kept up my TV, DSTV and Wifi for up to 4 hours. This was the case until December 2023 when I realized the battery only lasts for around 20 minutes. I raised the matter with BWH yesterday and was told that the item and in specific the battery has no warranty on and I will need to buy a new battery. Asking the cost of a new battery, I was showed a battery costing the same as what I originally paid for the inverter set, i.e. R8500 Although the battery that was shown to me is a lithium one there is no guarantee that it will last longer that the one I had in the inverter originally. This truly does not make sense as I don't believe any person will be happy to replace a battery every 6 months. Needless to say that I now have an inverter that will become pretty useless very soon unless I fork out another R8500 to replace the battery. The lady at BWH just pulled up her shoulders and said there is nothing she can do. This seems to me like just another money making business! I also raised a complaint on BWH website with no response since last Monday.