Thank you!
I sure hope I get more out of mine than that, but that is about what I get in a vehicle. The batteries are easily the most expensive part of a system.
Unfortunately the problem is over time all the sulfur cooks out of the electrolyte, turns to a solid, and settles on the bottom. so it is hard to get much more than that. You could dump it all out and refill it with new electrolyte but it is not worth the time, trouble, and added cost of electrolyte, disposal, labor, etc.
If you do the math. It is just cheaper to get new batteries for $100 a piece and be good to go for another five years. I don’t know how many batteries you have but I have 6. So my “power bill” is $120 a year for five years of life. Or $10 a month if the batteries cost $100 each. We get marine batteries from Walmart for that price because we are a boating area.