Eliminate standby leakage current of output capacitor in a DC/DC converter charging a battery
I would be inclined to use a PMOS transistor as a high-side switch:







simulate this circuit &ndash; Schematic created using CircuitLab

Select D1 to set the turn-on threshold voltage at the output of the charger, and select R1 to set the base current of Q1 to about 1 mA at the maximum charger voltage.

R3 and R4 serve to limit the VGS that M1 sees, and C2 can be added to slow down the turn-on.

Note that the MOSFET is connected "backwards" &mdash; the source terminal is connected to the battery, not the charger. This is a common configuration used in protection circuits.



If the charger capacitor doesn't bleed down on its own, you might want to explicitly control Q1, perhaps using the same signal that enables the charger.