Create 9v from two 3.6v Lithium Batteries?

[THATguy]

Is it possible to make 9v (or close enough) from two 3.6v Lithium batteries using a Joule Thief circuit?

[IanB]

It could be done using a boost converter, but there may be no point.

Fully charged you would have about 8.4 V, and discharged you would have about 7.2 V. This is within the range of operation of a 9 V battery, so many things that use a 9 V battery would work fine without any boosting required.

[THATguy]

Oh that's even better.

[Zero999]

Oh that's even better.

What do you want to power?

Ian is right. 9V batteries have a fairly wide voltage range, from 9.6V when fully charged and no load, to 6V when flat with the maximum current drawn. Properly designed appliances will be able to operate over this voltage range.

[THATguy]

Well it's a metal detecting pointer. So it may not even require 9v
I'm in the process of reverse engineering the pcb, so I can figure out how much it actually draws.
I the reason I wanted to change to Lithium rechargeable is to change the dimentions of the pointer.

[Dubbie]

no need to reverse engineer or take it apart.

Just hook it up to a benchtop power supply and turn down the voltage until it stops working properly.

[THATguy]

I need to rebuild it for changing the PCB shape.
Also like to redesign it too. - remove a few unneccessary bits.