Test eq cycle before after

In the European Union advertising has to show Carbon dioxide (CO 2 )-emission and fuel consumption data in a clear way as described in the UK Statutory Instrument 2004 No 1661. [43] Since September 2005 a colour-coded "Green Rating" sticker has been available in the UK, which rates fuel economy by CO 2 emissions: A: <= 100 g/km, B: 100–120, C: 121–150, D: 151–165, E: 166–185, F: 186–225, and G: 226+. Depending on the type of fuel used, for gasoline A corresponds to about  L/100 km (69 mpg ‑imp ; 57 mpg ‑US ) and G about  L/100 km (30 mpg ‑imp ; 25 mpg ‑US ). [44] Ireland has a very similar label, but the ranges are slightly different, with A: <= 120 g/km, B: 121–140, C: 141–155, D: 156–170, E: 171–190, F: 191–225, and G: 226+. [45]

I have a D8 flooded lead acid battery 1400CCA and 255Ah capacity. it is 6 years old on a boat with a 3 stage 12 amp charger which is on all the time when the boat is not in use.
battery is now very low in specific Gravity 1175 less than 40% capacity. it’s voltage 3 days after a full charge is .  this is far too high and we suspected sulfation to possibly be the cause of the higher voltage.(we read this somewhere)
we then overcharged it at 16 volts and it only drew 3 amps . After about 17 hours the SG had gone up to above 1200 about a 50% charge. a remarkable improvement.
my question to you all is why is the battery voltage still high on open circuit and why is there only 3 amps of charge at 16volts. should we continue to overcharge it ?
Hugh

Test eq cycle before after

test eq cycle before after

Media:

test eq cycle before aftertest eq cycle before aftertest eq cycle before aftertest eq cycle before aftertest eq cycle before after