The chiral magnetic wave (CMW) is sought using the charge asymmetry ($A_{rm ch}$) dependence of anisotropic flow in heavy-ion collisions. The charge dependent transverse momentum ($p_{rm T}$), however, could play a role as a background. With the string fragmentation models, including PYTHIA, we demonstrate the origin of the $A_{rm ch}-p_{rm T}$ correlation and its connection with the local charge conservation (LCC). The impact of $A_{rm ch}-p_{rm T}$ and its behavior in varied kinematic windows are also discussed. This study provides more insights for the search for the CMW and comprehending the collective motion of the quark-gluon plasma.