RS> It can be done. You are essentially just designing an UPS tho. The
 RS> tricky bit is the completely clean automatic switch from mains power to
 RS> battery power and back and keeping the battery charged. Again,

I thought a normal car battery recharger did this?  What about my $60 clock
that I just bought?  It runs off the mains and have 9V DC battery backup. 
BFN.

Paul

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