Both pterosaurs and birds have achieved gigantic proportions, with some species having twenty-foot-plus wingspans. I cannot remember ever reading about giant bats in prehistoric times. Did bats ever get anywhere near as big as the pteranodon or argentavis?
The bat fossil record is pretty sparce, so don’t expect much. Also, I don’t think birds ever achieved sizes anywhere near that of the larger pterosaurs while retaining the ability to fly.
I am not aware of any bats in the fossil record that were bigger than the largest present ones, the so-called flying foxes.
The largest flying birds and pterosaurs have evidently been scavengers or marine fish-eaters. These are niches that have not been exploited much by bats. There are no known scavenging bats, and there are only a few species that catch fish. Perhaps bats have been limited in their expansion into these and other niches by the earlier presence of birds exploiting them. Bats have a variety of ecological roles, including insectivore, nectarivore, frugivore, etc, but most of these don’t permit really large size.
The largest known flying bird, Argentavis, had a wingspan of up to 8.3 meters, or 28 feet, comparable to large pterosaurs such as Pteranodon, though not nearly as big as the biggest pterosaur, Quatzalcoatlus, which had a wingspan exceeding 12 m (40 ft), perhaps over 15 m (50 ft).
That’s one big-ass hummingbird. 
The wikipedia article says
Does that mean full grown birds had wingspans that varried from 5.7 to 8.3m or that the concesses estimates of it’s maximum wingspan vary from 5.7 to 8.3m, depending on who does the esitmating?
I believe those figures represent estimates of the wingspan by different researchers, based on extrapolation from living birds. According to this article (pdf), most researchers agree that the mean wingspan was 6.5-7.0 m.