For those who are interested in replacing the battery with a 2000 mAh battery that provides longer battery life, purchase it from this company
http://www.atomsindustries.com/ASD1258 or their EBay storefront
http://m.ebay.com/itm/171462122567?nav=SEARCH
A number of people have said that 2000 mAh battery sold on EBay and amazon and marketed to work for the DS4 are counterfeits
You need to swap the wires to the JST connector of the 2000 mAh battery to match the configuration of the one that Sony provided in the controller. Really easy to do, follow this guide by reddit member AtariXL.
http://m.imgur.com/a/97f3s
You don't need to cut away any of the plastic area that holds the battery in place nor use glue/tape to adhese the battery to the plastic. Fitting the battery in there will be a tight squeeze, but it'll settle in just fine once you snap together the two ends of the controller again. Just remove the reset button because the battery will push against it. Be sure store that button in a safe place like a ziplock bag.
I've been playing with the controller modified with the new battery for 6 hours now and it's only down to two bars out of three. People have said that they have gotten 12-14 hours out of it. Huge improvement in my opinion!