I own a 2006 Ram 3500 CTD 4 Whd that has both the original batteries in it, they acted weak last winter when trying to start it without the block heater hooked up so I went to the local Wal Mart and bought two new Duracell, maybe Everlast, which ever ones Walmart sells, replacement batteries. I plugged the heater in and those batteries are still in the truck now starting it okay.
My message is try to find out who makes those Dodge CTD OEM batteries and buy them
The OEM batteries in my old 1998 Ram 2500 1/2 CTD truck lasted 11 yrs also before one went bad, the other one lasted 9 months longer