with a low vgs you may find the vds voltage drops across both mosfets may exceed the .3v from a low vf diode .(your vgs maximum is vcell how low will it be with a flat cell).either way the battery is likely to undercharge not overcharge .(the charger sees vcell plus 2x vds)or (vcell + vf)
how does this "charger" sense when the battery is charged , if it looks for the knee in the cell charging voltage then any series resistance between the cell and the charger may distort this process with less than ideal results