First off, let me ask you what type of battery are you using? Are these true deep cycle batteries or the “deep cycle marine” type batteries? If they are the marine types then it is likely that the batteries are just at the end of their lives and nothing can be done to restore them.
I have spoken with the folks at my local golf cart shop and the tech support people at Trojan and they both tell me that the electronic battery life extenders do not work. Also the chemical rejuvenaters can’t restore a damaged plate. They can help remove sulfide crystals, but if the plates are covered with lead sulphide then the plates are pretty well shot.
The best advice I can give someone (like myself) who lives total solar for power is to get good quality deep cycle batteries and not to draw then down below 50% DOD. I have 8 Trojan T-105’s arranged in two sets of 4 to give me 24v @ 500ah.
If you did want to do an equalization charge you could isolate 2 of the batteries from the inverter to run the house and equalize the other two. Then swap for the other two the next day.
Here is a piece of advice for bargain prices on batteries. Go to your local golf cart shop and ask about used batteries. Golf cart batteries are true deep cycle batteries and many rich folks will change out their batteries every couple of years just so they never have any trouble with them. My local shop sells the used batteries for $20 each. Just take a volt meter and a battery hydrometer to test then and make sure you get some good ones. As long as the specific gravity of the electrolyte is 1.26 or better you will get plenty of life out of it.
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