It turns out I screwed up big time in designing and using my solar electricity system.
First of all, I have the wrong controller. My Concord 4G AGM batteries want 14.4 to charge and 13.2 to float (similar to a wet-cell), and no equalize phase. My Morningstar ProStar 30 controller provides only 14.0 in GEL mode and 14.15 in SEALED mode, which is too little to actually charge up the batts. It'll equalize in SEALED mode once a month a 14.35v, almost up to spec, but only once a month. Worse, the Morningstar float charges at 13.7, which is too high. I had the thing set to GEL for nearly a year, which is wrong-- my batteries haven't been a full charge since I bought them. That's a sure way to destroy batteries-- they get sulfated if they're not quickly charged back up. Another problem with PWM controllers in general is that they aren't very efficient when winter comes. MPPT controllers are better for this; they get up to 40% more efficiency on cloudy days or short winter days.
Second problem is that winter is definitely here. The rains have come, and we went weeks with no sunshine at all!
Third problem is that my lifestyle had become accustomed to having nearly limitless electricity. I'm on the computer for 4-8 hours in a night, and in the summer the batteries would recharge enough that I never noticed any problem. I continued that pattern during the week when we had no sun, because I had to. And now my batteries are fried. I have been over-discharging them, every day, and under-charging them.
When I bought these batts they'd show 13.1v after sundown, and I'd hardly ever get them below 12.9v. I deep-discharged them in May (parked next to a tall building in the partial-shade all Memorial Day weekend, but kept hacking away anyway), but they'd start the night at 12.9v and hardly get below 12.7v by morning. Now they won't charge past 12.7v, and I can get it down to 12.5v in a typical night, and into the danger zone (12.2v) really easily.
So I'm doing a couple things. First off, I've changed the setting on the ProStar to SEALED to get it closer to spec, and maybe even equalize it. Secondly, I'm buying a MPPT controller. Thirdly, I may buy a plug-in electric charger (that'll handle high amps-- I have 440Ah of batteries which would require a 60A-80A charger), to hopefully bring these batteries back to life quickly, and serve as a backup in winter. Finally, I've ordered a low-power-consumption Asus EEE laptop to use for websurfing and 90% tasks for which I don't need the full power of my 2.33Ghz Dual-Core Intel laptop.
We'll see. But my biggest fear is that I've destroyed $1000 worth of batteries. I hope that I can get out of this mess without that kind of expense.