i have one of these
https://no.co/products/charging the 26000 has a "repair" mode that brought back a couple deep cycle that would not charge above 11.7 volts. it took like a week in repair mode to restore them, but they would charge to 13v+ after the week or so. i understand this time frame may not suit your current situation, but these chargers are great with multiple charging modes and options.
regarding the solar charger, i was left one by the previous owner of my house on the generator and has worked flawlessly. the generator battery is a small motorcycle type and has not shown any sign of over charging or damaging the battery.