It's been running fine for a year. I put the system together last September. Within the last two weeks things have changed to my current desperate condition.
It has clearly not been running fine, as your indicated voltages are far too low.
Most likely the batteries have been damaged. You might be able to improve things with a desulfation cycle.
As others stated I would suggest you add more solar panels to the mix to ensure they are fully charged each day. If you do not fully charge lead acid batteries each day you will develop issues over the long term which will slowly get worse and worse, as you suggest to be the case.
[As you can see from my handle, I've unsubscribed from this forum. (As a protest against overzealous Moderator moderation. (No option to delete my account.)) But I'm making an exception here to help others.]
The OP's problem is, at least in part, his Mighty Max brand batteries.
I ordered a pair of Mighty Max batteries from Amazon in 2020 for two different UPS's. Both batteries failed in a year. (Whereas I have typically seen 2 + years with other brands.) And these Mighty Max were supposed to be 9 A hr! (As opposed to 7.5 A hr for previous.)
So when the OP said that his batteries are failing after a year ...
I left a one-star review on Amazon to warn others about MM's poor longevity. But my review has mysteriously disappeared from Amazon.
So I post here in the hope of more permanence.
Lead acid batteries can last a long time with proper care and usage. If you are using them to their limits or beyond they can be ruined in 6 months. Its also pretty hard to screw up their design so badly that they have a significantly shorter life than other designs.
So first and foremost, I will point out that your anecdotal statements are not proof of anything without far more data on the matter.
A lead acid battery in a UPS should last several years unless its being cycled constantly, or is being overcharged very badly by that UPS. If your UPS is killing batteries in 2 years or less then the UPS or installation environment is most likely the source of the problem. Most UPS batteries last as much as 5 years if used sparingly and its not uncommon to see 10+ years.
If your UPS units are constantly at high temperatures (which means basically anything over 85F) it can ruin the batteries very quickly. This is common in server racks with bad ventilation and hot server rooms. Again, this is not the fault of the battery itself.
It sounds to me like you are going out of your way to criticize this specific brand by searching forums and complaining in other people's threads.
It also sounds to me like the issues you experienced are user error rather than the manufacturer's fault.
Regarding moderation, you are out of your mind if you think its "overzealous" here. This is the most laid back moderation team I have encountered in over 20 years of using forums, of which I spent my fair amount of time as a moderator myself on a board with several thousand active users (back in my paintball days). I suspect a common factor is present.