Sealed flooded batteries do not belong on a boat, especially not for "leisure" or house batteries. These are not deep-cycle batteries, no matter their markings.
The Victron Centaur is a capable charger.
As was suggested, replace the batteries you have....both of them...with golf-cart batteries which can be found most anywhere. Trojan T-105s are the "gold standard", but there are many others. A good U.S. brand is Crown...made in Ohio
Two 6V golf-cart batteries in series will give you about 225AH capacity @ 12VDC.
They should be charged at 14.6-14.8VDC in the absorption phase, and when fully charged should be floated at 13.4-13.6VDC.
Treat them well and you'll get 5-7 years from them.
Do NOT discharge below 12VDC. Better, keep them as fully charged as you can, and don't discharge below 12.2VDC (50% SOC).
Use only distilled water
to keep the electrolyte about 1/2" above the plates. Be careful not to introduce contaminants when you fill them. Keep them clean.
Get a good multimeter and clamp-on ammeter, and learn how to use them. Don't believe the onboard meters unless you have checked them against a reliable standard.