Unable to boot from USB with battery attached

I inherited a 13-inch 2012 MB Air A1369 (1.7 Core i5) with liquid damage. It came without a SSD. After cleaning I am able to boot from a USB HDD with OS X 10.8.2. However when I connect the battery all I see is a blinking question mark on a folder. Disconnecting the battery allows me to again boot.

Do I need a SSD to allow for operation when battery is attached? Are there other problems? Would sending it off for repair be helpful?

I just finished installing a SDD, connected the battery,restored from an external backup and it booted. Weird!

Without a working Power Button an SMC reset is impossible.

Now, to replace the keyboard. Onward and upward.