A synaptic vesicle belonging to the pool that repopulate vacancies within the readily releasable pool (RRP) of synaptic vesicles, and require more significant stimuli than the RRP in order to release neurotransmitter; about 10-15% of the total number of synaptic vesicles at a resting terminal bouton are in this state. [ http://www.ncbi.nlm.nih.gov/pubmed/22745285 GOC:pad ]