I would suggest a higher capacity charger for those emergency moments. 1.25A will barely make a dent in big deeply discharged batteries. At a voltage of 12.9 it may not have reached it's maximum charge. Was the battery voltage still rising or did you just stop at 12.9? Normal charging with a smart charger is to take the battery up to at least 14.4 until the voltage stops rising. A float (maintaining) voltage is usually around 13.2 or so give or take a decimal or two.
I suspect the battery has reached or past it's "best before" date.
A hydrometer will tell you the real story.
