http://guitarelectronics.com/product/PMTXBAT9 It is a separate battery box for active basses. This would make it really easy to parallel 9 volt batteries, and give you a TON of battery life.
Someone's got to have seen this. There was a thread the other day about an external active bass power supply.
One more thing hanging off your bass. It's much easier to route the bass than do this. However, it's got a place in vintage instruments. That's about it that I can think of though.
I think its a pretty good idea, I don't think it hangs off the bass. Looks to me like you'd sit it on your amp, pretty much like an external DI. For bass players I think it'd do nicely if you could provide voltage, what with every man and his dog wanting 18V. A second 9V inside there with an internal DIP switch. However, if you use battery instead of their clip you already have 18V. US$69 probly makes it like $100 here, thats a bit steep for what I'm suspecting it contains. Josh D