CMOS memory <--- lithium battery?

[yousufferbutwhy]

This would be my first attempt at doing anything at all with a digital IC, so pardon my naivety. And the application probably has little to do with the fact that it's digital, but I'm hesitant to guestimate my solution and figured this would be the best place for the question.

I'm in the process of restoring a Boss DR-55, the first ever drum machine produced by Roland. I had the thought of adding a lithium battery, so that I can use an external power source and retain patterns when not plugged in. It uses a TC5501P-1 chip for storing patterns, though mine actually has a NEC D5101LC. There's almost nothing substantial to be found in the Google black hole of searching for obsolete parts on the D5101, but from all I can tell, they're equivalent. There is no other difference in circuitry from mine to the schematic, aside from having fixed resistors in place of a couple of trimmers in the sound generation circuitry, which I've already swapped out. I suppose this was an early revision, but it was quite banged up when I got it. No serial number, and, well, part of my restoration is bridging traces across a hairline crack.  But everything checks out OK so far.

The battery pack +V has a series diode, then meets up with a parallel 22uF electro cap to ground, to hold on "for a few minutes" while changing batteries, both connected directly to Vcc.. The 5501 datasheet says it has a minimum 2V data retention voltage. SO, I'm thinking a standard 3V lithium battery used on motherboards etc. would do the trick. But I'm just a little confused about how to implement it. I've been wondering if some kind of switching circuitry would be needed so as to not drain the backup battery current or overload the operating voltage while it's running. But perhaps it's as simple as connecting it in parallel with the battery & electro cap? Yea, I feel a bit thick right now. I'd appreciate any help.

Thanks,
Ry

[toneman]

i know this is an old post. but I just was perusing the old messages....

what U need is a complete schematic...
after a little googling, I found the schemo and a bunch of info here...

http://fa.utfs.org/diy/boss_dr55/index.html

After a quick look, the unit runs on 4 x 1.5 cells = 6V.
D5 is a "reverse polarity protection diode".
It looks like the batteries are always tied to the memory chip, IC1.
Switch8 (SW8) is tied to the volume control. 
So it looks like when U turn off the output, the volume is all the way CCW.
BUT, this does NOT turn off 6V power to IC1.
I cannot understand why U would want to add another battery (lithium) when the DR55 runs on batts anyway(?)
I see no provision for an external power supply(?)   Did U kludge one in?
The main thing about power supplies and batteries, is to make sure the PS cannot charge the batts.
Lithium & ordinary alkaline cell are NOT meant to be charged.
So adding another diode to "OR" the Power Supply into C39 would be the way to go.
I should mention that the PS should be regulated, not just a wallwart.
I don't know how much voltage IC1 can take, and U only get one chance..
good luck!!  on your repair/mod.
afn
T