Can you please explain what kind of batteries are you using?And what are your usage patterns? For example I'm using two 12V 200A lead batteries, I'm trying to use then only on 30% discharge so that they will last longer.
They're nothing special, just heavy as hell lead acid batteries. I also try to never discharge too low...my rule of thumb is 50%, though I've run them until the inverter shut off due to low power. So, I've obviously gone below 50% a few times. They're three years old, and starting to show signs of degradation. I bought them at Costco for, I think, $98 each, and I'm pleased with the return on investment, given that they've gotten me out of being stranded on more than one occasion (I'm in a motorhome, and the chassis battery has been an interesting component, having more than it's fair share of failures, always in very bad places to have a motorhome that won't start).
I should point out that when I am off-the-grid, I am extremely conscious of my power usage. I charge everything during the day, religiously, so that I don't even have to turn the inverter on, some nights (lights, fans, water pump, and fridge igniter are 12V). It's a ritual...actually, it's a really satisfying ritual that I miss when I'm living plugged in. I need to go get lost in the desert or in Mexico this winter; been parked too long.