[SOLVED] lowest drain-source voltage for mosfet

When I run multisim, I noticed that MOSFET such as IRF9630 or IRF9510 has minimum operating voltage (drain-source) of 4 volts. I wonder if there is a MOSFET with lower voltage such as 2V. I am attempting to design a battery charger but in unique way such that the source - generator does not see the load except for the capacitor. The source generated range about 2V to 12V. The lowest range is important.

I attached the image here. The battery voltage is 1.5v not 9V.
So switch 2 is on and charging the capacitor and at the same time switch 3 is off and battery is not charge. Switches (mosfet or transistors in optoisolators) are turned on/off by external timer. Switch 2 is on and SW3 is off then SW 2 is off and SW3 is on. So that battery is isolated from battery. The generator does not like low resistance / impedance. However the battery is low impedance and so is high capacitance capacitors. I can get away with low capacitance capacitor. That is why I ask if anybody got experience with switches at low voltages that require low power to activate. So far I know of MOSFET, Optoisolators and darlington. My current problem with MOSFET is that drain source voltage is minimum 4v in order to operate (IRF9630 and IRF9510).
Thanks.

I don't understand what you mean with minimum drain-source operating voltage. I can't relate it to known MOSFET properties. Of course a minimum gate-source voltage is needed to switch the transistor on. But Vds can be as low a millivolts.

Could you explain how you have arrived at the conclusion that the MOSFETs need 4V from drain to source to work?

Keith

I think I know my mistake. Maybe the voltage limit was set by LED I used for testing. see image .

I don't know if that circuit is something you built or just simulated but either way you should have resistors to limit the current into LEDs.

Keith