The use of AA batteries is okay. The only reason to go for proprietary batteries would be battery capacity. What is IMO really missing is a battery charge circuit. A Gp2x runs at least 3 hours on batteries, which is more than many laptops do. However, the lack of a charging circuit makes the Gp2x less mobile, it cannot switch from AC to batteries without reboot and when you arrive at location you cannot plug it in and continue. Instead you need to remove the batteries and put them into a charger. With a charge circuit, your Gp2x would always be fully charged when at home, and you could simply take it have have several hours of mobile fun.