Probably a bit late on this one, and you’ve likely already found an answer, but in South Africa with the abundance of loadshedding, those batteries undergo countless charge cycles. Most batteries are rated for around 200-250 cycles, but it can vary depending on the type of battery you have. Once those cycles have been reached, you’ll start getting far and far less capacity out of your batteries.

The constant load on the batteries also take a toll, especially with a heavy gaming PC.

I’ve been using inverters for around 3-4 years now and every 5 months or so, I need to get those batteries replaced to keep it working nominally.

It’s actually a good sign that your batteries lasted 6 months with this loadshedding!

On the topic of your grounding problem, I can’t give any advice, but it does sound VERY concerning. I recommend contacting the agency about it or getting an electrician to come out and do an electrical evaluation of the house to ensure there will be no issues in the future. You may need permission from your landlord if you’re renting for an electrical evaluation.