I agree with previous on trim limits.... as to where to find same, I think you will find in limitations. I also could not find them written down but they are displayed on a representation of a load and trim sheet for the indivdiual aircraft.
As for flight on BAT after gear extension.... I believe this problem has been rectified with the new series of 320 and is not a problem on the 321. On the older series A320 you had to be aware of the fact that the rat would stall at speeds below 140kts. So in the event of prolonged flight on BAT then considerations to systems which are a high load on the bat i.e.probe anti ice. These are located overhead on the emergency panel and are useually collered.During a go around If in fact the gear retract system does fail then you must fool the aircraft into thinking it has retracted the gear. You do this by pulling the LGCIU sys1 cb overhead and then need to accelerate to a min of 180 kts to restart the rat. This reconnects the csmu and saves bat life. Hope that helps (these can be found in fcom 3 abnormal & emergency)