The NEW type battery chargers are nothing like the old type that gave a constant charge, the one I've got (CTEK 7000) can charge a battery on the car without doing any damage to the onboard computer alarm etc. even a dead battery has been given a second chance. It'll charge lead acid, wet batteries, MF, AGM, and most gell bateries. They pulse charge, and when on reconditioning they push 15.7v into the battery.
But they aint cheap I think mine was about £70. but batteries arn't either! especialy for a Diesel. I recon it's paid for it's self again and again
In the 70s we used to put a spoonfull of Epson Salts per cell in lead acid batteries and give them a high charge to release any sulphated cell's.