Yes the books will be required to be maintain...
Section doesnt sets out limit for business... It sets out limit for assessee..
So if assessee's gross receipt from business (all businesses) exceeds the limit, 44AA will be attracted.
Let me give u an example..
Dont think of individual.. Lets say there is a company.. The company is engaged in two businesses.. One is commission and other is trading..
Now, when u'll make p&l of the company, u'll show both on receipt side..
Same way consider an individual as one unit.. When we prepare b/s of an individual (not a specific business), we'll have to show all the receipts.. Section doesnt say the gross income from "business" shall not exceed the specified limit.. It says gross income of "assesse" "from business" shall not exceed the limit..
NOTE: I've assumed that the gross receipt of commission business is more than the 44AA limit (as u haven't specified it)