The O.E. battery is a genuine Optima spiral wound AGM battery. If you purchase an O.E. replacement through the Stealerships you are going to be paying a lot of money. An O.E. CRD battery - at least up here in Canada - is priced like it uses gold instead of lead.... I was quoted over $400.00 CDN when I priced one out about 4 years ago.
The problem as I understand it is the charging system of the CRD is designed to charge Absorbed Glass Matt batteries. AGM batteries have a different charging characteristic than traditional acid bath batteries, and you should therefore replace your battery with another AGM battery.
Try a NorthStar or Odyssey battery... you can get them sometimes from mass retailers like Sears of Canadian Tire under the retailer's own label, (the Canadian Tire version of the NorthStar Battery is the Motomaster Eliminator Ultra XD Pure Lead battery, and has a grey case with a bright blue top). If you can find one they are generally a little less money than the NorthStar or Odyssey branded identical twins.
Both NorthStar and Odyssey batteries are Absorbed Glass Matt batteries that use a newer generation of robotics to assemble and compress the lead onto the grids in a traditional flat plate manner. Because the cells are compressed, no calcium is required to help the lead stick to the grids, and therefore the chemical reaction between the sulfuric acid in the glass matts and the pure lead is stronger, creating more electricity. The AGM technology also makes the battery spillproof... Freezing the battery, even when it is completely discharged, will not harm it.
The previous generation of AGM batteries that had compressed cells required those cells to be rolled up or spiral wound in order to be compressed. While this made for a interesting shape to the battery, you lost valuable space in between the cells for more lead and acid. If you lift up a group 78 NorthStar or Odyssey battery and compare the weight of it to the Optima O.E. battery, (also Group 78), the O.E. battery is roughly 5 lbs lighter. The specifications of the NorthStar/Odyssey batteries are therefore superior, simply because they have more lead and acid for the same size battery than the Optima battery.
I also understand that the Optima batteries are now made in China, and do not have the same level of quality that they used to have. NorthStar and Odyssey batteries are manufactured in the U.S.