It sounds like this trick can only be done with a 12V Duracell security battery. However, it does seem to pop out 8 batteries that cost four bucks a piece on their own.
The hack uses two 12v security camera batteries, a cheap car charger, some solder, heat shrink tubing, and a pack of blocking diodes to make sure the power is regulated. You will need some basic soldering skills, but the process itself isn't as overwhelming as you'd expect. In the end you'll have an external battery capable of adding around six hours of life to your laptop for a mere $60 instead of the $200-$250 you'd pay for a retail version of the same thing. As with any electricity-based DIY, be careful if you try this one for yourself. Hit up the forum post on The Verge for a breakdown of materials and guide.