Bench PSU from Drill Battery

This design is for battery model;- MB10.8-13 Lithium battery used in MacAllister portable tools which are available in the UK from B&Q.
The DC - Dc unit can be purchased for a few £'s here;- http://www.banggood.com/DC-DC-Step-Down-Power-Supply-Adjustable-Module-With-LCD-Display-With-Housing-Case-p-1038740.html.
This PSU will give you a smooth and constant voltage between 3 - 30 volts.
Obviously with a 10.8v battery you are limited to a top end range of 10.8, so I am working on a design for a