Question

How long can you keep open beer in the fridge?

Answer 1

You can keep it for as long as you want; you're the boss of your fridge. 
But anyway, an open beer bottle can stay good in the fridge for up to 96 hours, probably more. 

Answer 2

Depending on the beer, it can last anywhere between 96 to a week

Hope this helps! A thanks/brainiest answer would be appreciated :)