AD-20/PS2 External Power Solution includes:

9.6V 1000 mAh Ni-Cd Battery - 6 hour run time
5 hour battery charger with auto shut off

Plug and play.  
Extra batteries sold separately.  
Call or email for details.

The sales pitch -- I was running my ps2's and ad-20's on 9V up until the battery up and died mid set this past summer.  NO WARNING.  Looked down at the deck and there were no levels.  Died right in the middle of Ralph Stanley singing Man of Constant Sorrow.  Yup, that was me that day.  But no more.  I run these babies now.  Insurance? Yeah.  But over time they will pay for themselves in more ways than one.
 

$50