Hello,

I want to design a simple circuit which connects a 3.35V battery to a circuit, when the input voltage falls below 9V or exceeds 35V. Please help me out.

 

Sounds like you need a Window Comparator. Try Google.

 

It will not be simple...
With the few informations you provided, you will need comparator, voltage references, relay, relay driver, etc...

 

More details please. How is the 3.35 battery related to the "input voltage"?

Are these isolated circuits?

Explain exactly what you plan to do. It is probably not too complex.

please provide

1. current from the "input voltage"
2. current from the 3.35V battery