Since it seems that your batteries may be suffering due to a improper charge regime, if you have a such a bench top charger that puts out upper 14.9 to lower 15.x volts, you might consider putting a say 30-40 min or so cell-equalization charge on the T-105’s to help drive the sulphate from the plates and back into the chemical soup solution…(Be sure to loosen or remove caps…).
FWIW, I would agree that in your application the ‘single’ 100w panel is a toy - hopefully your batteries function can be restored…
3 tons