Why only 4 stars?

Excellent! Note that the item is not sold or delivered by Amazon and the company (specializing in batteries for many years) only enjoy the excellent site.
If there is a product for which the "mark" is significant, it is a battery. For what she is hiding inside? Certainly it is wary of "labels" but Varta is a certain guarantee of seriousness.
Conclusion: we are wary of cheap batteries ... but other, at prices so low that this not but unknown! We find many service stations ...
What there was remarkable for this article is that equivalent models without known name, were even more expensive in nearby shops!
And when I say "equivalent" ... not even as this Varta has a capacity of 52Ah, so that most are 50 or 48 Ah.
Finally, strange thing: I contacted (by telephone) company that sells and delivers. Pleasant welcome, and keep you well: the object was more expensive home than DIRECTLY purchased by Amazon ... which says a lot about all the business is done behind our backs!
But if it goes in the right direction, it's not too serious ... in the short term.
In short, very good article, so why 4/5? Because more than others, it must also be subjected to the test of time! So go to 4 years ... if I think about it!