is reatsu quantity = AP energy? nah, prolly not. otherwise, there wouldnt be the need for named attacks, training to hone it, training to use it more effectively etc, cuz then, one could just dish out their reatsu that that would be it. so no. reatsu is likely below one's full AP. think of how u can 'reatsu crush' someone by showing it a lot, while u can kill them by using it on/as a technique. kinda like aizen and normal humans- he could disintegrate them, but he couldnt do anything to ichigo with it even when he was far more powerful, and completely pissed, but the moment he used a named technique, he hurt him (that explosion).