Shop for a 49/H8 battery...it should have the specs you need to operate your e53 X5 with not problem.
As others' mentioned...you'll mostly run into a battery brand made by one of 3 battery manufacturers for the USA market. The specs can vary slightly...but where one may be a bit more in one spec, it may a bit less in another spec...overall making the batteries pretty similar.
The e53 can also use a "wet" (lead acid) battery or an AGM battery. You'll probably find that the AGM battery costs approx $20-$50 more...but either way...again, look for the 49/H8 battery class size.
You can see the Duracell 49/H8 AGM battery semcoinc posted in his reply above. Back in 2015...I got the "wet" Duracell 49/H8 battery from Sams...and you can see in the East Penn battery chart below...what the specs are for the wet/lead acid & AGM batteries are. Duracell brand batteries are made by East Penn/Deka. The Autozone's, Advanced Auto's, and Walmart 49/H8 batteries are made by Johnson Controls. And you'll also run across batteries made by Exide (BMW, Bosch...to name a couple):
