I had this exact thought about running off a battery.. I coin it the Energizer Bunny!
I had also thought that maybe there were some sort of Scripts that could run in standalone, post-exfiltration. Things like running hashes against smaller wordlists or something to speed up credential hacking. Don't really know if the BB is powerful enough for that but it's worth looking into.
Try flashing the latest firmware via the web interface. I saw a similar issue with my pineapple when i first got it. wlan1 would not stay enabled. Firmware 1.0.4 has been running smooth for me though. Hope this helps.
Older article... But who knows maybe it could be a reality someday...
http://techcrunch.com/2009/07/23/only-in-japan-kddi-shows-off-wireless-microsd-card/
or
Maybe this could work..
http://eshop.sintech.cn/sd-to-micro-sd-fpc-extender-with-65mm-flex-cable-p-764.html