And if you don't win, you can always use those batteries for the GB you already own...
NintendoWeb reports that you can enter to win a GBA (and receive it on March 21) with the purchase of at least ¥1000 worth of Panasonic batteries. In Japan, anyway. Maybe you could import the batteries, hmm?
It was announced today overseas that National/Panasonic is beginning a promotion in which some lucky consumer could be among the first to own a Gameboy Advance system. Before any of you ask, this does not mean Nintendo's next portable system is coming out earlier than expected, it just means someone is guaranteed it. From the looks of the pre-launch hype, that could turn out to be a valuable thing.
The promotion involves National/Panasonic batteries and the year 2001. As far as the batteries go, consumers who buy 1000 yen ($9) worth of them have to save the bar codes, then send them to a specified address. The year 2001? That just means there will be 2001 winners.