E53 X5 3.0d negative battery cable is #10 in the diagram below. Click the link and scroll down to #10 and look for any info in the supplemental column that mentions anything about an IBS (intelligent battery sensor). BTW, you won't find it because again, this technology didn't appear until the e70 X5.
E70 X5 3.0d negative battery cable is #1 in the diagram below & if you click the link you'll see the mention of the IBS listed in the supplemental columns. The mention of the IBS is important here because owners need to know that this sensor is required in the e70 set-up.