charging deep cycle batteries?

[72Impala 10+ year member]

The charger charges high at first to " desulfate" the battery. Then it goes down to normal charging voltage. This is how most of the battery tender/Schumacher Agm chargers work. My x's power intellicharger does not charge above 14.4 on the 12volt mode. From what I understand the XS power charger uses a different method to desulfate than high voltage. Me, I would not want my 12v batteries seeing above 15.5 volts ever. Mine have never even seen over 14.4, ever, and they float at 12.85 after sitting for 4 days with no charging (4 year old batteries).