In an interview with Nintendo Online, Yoneyama talked about the issues he and design partner Tomoyuki Sakiyama faced including battery life, durability, reducing size and weight and maintaining the machine's balance.
On Balance and Weight
"It's not just a matter of making sure all the components can fit in the case. We also have to think about the total weight and how the machine balances from front to back and left to right when the user is holding it."
On Size and Functionality
"We knew that we couldn't make it so small that we sacrificed functionality. Of course, we wanted to keep the display the same size, and it wouldn't have worked to change the button positions much either. To reduce the size within those constraints, we worked together with component makers, and now we're using some custom-designed parts."
On Cost Implications
"We had to be very careful about adding cost to the finished product, and were also aware of the possibility that some factories may have trouble producing our parts. Taking these issues into account, working out where it makes sense to use custom parts is something that we lost a lot of sleep over."
On Battery Life
"The battery looks the same as the DS, but it actually has 20 percent more storage capacity. The DS Lite screen is so bright that it might be a little uncomfortable to play in a dark room. To address that, and to offer some power savings, we added four selectable brightness levels to the DS display."
"For a portable console, you can't afford to neglect durability. Rather than having our users pay several thousand yen to fix the console if they drop it, we'd rather that they be able to spend that money on buying games instead. With that in mind, we've beefed up the internal structure and layout, and we've spent a lot of time doing strength testing. Of course, when you strengthen the device, you also struggle with weight and size...that's a conflict that's been with us since the time of the Game Boy."
Translation: Thanks to Gamespot.