Vintage Simmons Drums (UK) Users Group

I have an SDS-7 and as long as it is powered it works fine.  When 
unplugged for any length of time (a few hours) all is lost.  I realize 
this must be a battery problem.  Does anyone have expeience with this 
who could explain how to locate the battery and or batterys and change 
them.  Is there a battery on each card module or only one on the main 
board?

thanks in advance 
Barry