Diode advice (charge & drain circuits)
Generally, all that is needed is a single diode to prevent discharge back into the charge circuit when operating on battery power only. The disadvantage is that you lose a diode forward volt-drop when charging but this (generalism alert) is not normally a problem.

I would also advise that if the battery is a raw (ish) cell then under-voltage protection might be needed to prevent failure of the battery from too much discharge into the target load.