I presume you are talking about acoustics that have a pickup built into them, although it doesn't really matter either way..........
You still need to plug them into an amp or PA. The inbuilt preamp is there to boost the miniscule signal coming from the pickup up to a useable level and "active electronics" (ie: having a battery) is preferable to "passive electronics" for this purpose. Whether or not passive or active is needed is largely determined by the type of pickup used.
Are you saying you have an acoustic that has a battery in it?
If so, does it have preamp controls on the guitar?
If so, I think you are saying there isn't a visible jack socket to plug the thing into an amp with.
So two things..........firstly, if there is a strap button on the end of the guitar, check to see if that is also the jack socket, secondly, what kind (brand, model, etc), of guitar are you talking about?
Its a takamine Acoustic Electric guitar. It does have preamp controls, but i do not see an input to hook it into an amp, only a place for batteries to go.
Did you find a 1/4" hole in the strap button? This pic is the type of combination strap button/jack socket that Takamine use on their guitars...................when they first came onto the market they fooled a lot of people.