Battery Problems

My starter battery won't hold a charge. It's fairly new (only about 2 yrs) I thought it was my deep cycle battery so I changed that, then I changd the fuses from my charger to my batteries. Got enough charge to turn the motor over and start with no problem. Drove it around the lake hoping my alternator would charge it back up. Once I stopped it had no more charge. Luckily I was able to pull start it. Can you help?

ANSWER
Starter battery is probably sulfated and will require replacement. If any starter type battery ends up deeply discharged it doesnt last long after that. You do need to check the charging as many fail due to under charging and never being fully charged