Using Li-ion laptop batteries?
 

Is it feasible to use li-ion laptop batteries as a power source?
Can they be charged using an off the shelf smart charger?

I ask since laptop batteries are considerably cheaper to purchase than other batteries for the same capacity

Anyone?

A battery is a battery as far as voltage goes. If the laptop battery has the proper voltage and a high enough capacity for your system, I don't see why it wouldn't work. Making the connections to the system may require some McGuivery and some soldering. Make sure you get a charger that is compatible with the Li-ion chemistry, however. The charging regimes are different for the Li chemistry.

Instead of a laptop battery, find one of those external li-ion portable DVD player batteries. I used one for a while before replacing it with a larger pack from batteryspace. The battery was designed to provide extra power for those portable DVD players. It had a built-in charge controller, so all you had to do was plug in a wall-wart transformer to charge it up. It featured an LED battery level indicator. It was rated for 9V @5400mAh. I got it for less than $40.