The purpose of these battlebacks is to prevent the "looping" of battlebacks that occurs when increasing your game's resolution to 1280x720.
I do not want any credit for this as they're just RMMV default resources, enjoy! Free for use and no credit required for private or commercial products.
Spoiler

http://www.mediafire.com/download/6mr9r0znn99bu6m/RMMV_default_battlebacks.rar - Original size battlebacks