BlackStar SuperFly Extension speaker powering off.

[PhatBeachDaddy]

I decided to get a BlackStar SuperFly busking/party entertainment PA. However, when running the system, using battery packs only, the extension speaker keeps turning off after approximately 30 seconds. I solved the problem by also plugging in an old iPod to the extension battery as well. Is it possible the lack of electric draw by the extension spkr causes it to power down? Is there a feature of the system I’m overlooking?