Hi,
You can buy this for 99$.
More here: http://www.coolest-gadgets.com/20071001/coleman-recharging-tools-in-a-flash/ (http://www.coolest-gadgets.com/20071001/coleman-recharging-tools-in-a-flash/)
Not really OU but may help to build one faster :)
Let's disassemble one and have a look at charge/discharge electronics.
Regards,
Chris
Nice. My battery powered tools are always discharged when I need them, and often it is for drilling screws. $100 isn't too bad to make life simpler.
j