Earlier quoted context omitted.
Yep, the Nintendo 3DS came with a 1750 mAh battery and that lasted for 3-5 hours. Get a small power bank or a 10,000 mAh one and you're set for the whole day. I don't think battery is too much of a problem.
Y'know, the correct solution would be that it came with one
On the other hand, I think it could be a nice touch to give the customer an option to buy a case/battery combo, designed by the same manufacturer.