Your 663 is an uprated 643. Lucas have gone bust. It has a higher cold cranking and ampage. Whenever people buy batteries they seem to go for the higher ampage. Don't. Buy the largest battery you can which will fit. Batteries are like people: if you ask them to do too much they'll tell you where to go. Pay attention to the CCA (cold cranking). Its the CCA that gets your starter turning and thats what you want, especially in cold weather and with diesel engines. The 663 should start your engine no problem. Forget leisure and marine batteries. Totally different set-up. And as for agricultural dealers: yeah you can buy one from them. But they use the same batteries on tractors etc. as they do on wagons and Land Rovers. Theres no such thing as an agricultural/tractor battery. If you go to a local dealer you would be looking at about £90 for a 663. Depending on how much you want to pay: Numax - Varta - Odyysey. PS. Have you checked for faulty earths and your alternator? Don't buy online. If it screws up you gotta post it. And carriers aren't insured to carry lead-acid batteries. Marine and leisure batteries. They're designed to be discharged & recharged on a regular or irregular basis. You can take them down to 15 or 20% capacity and bring them back up to a full charge. But thats another story.