Ram backup battery question,

[Theo]

Hi, list.

I'am looking for backup batteries for some low-voltage cmos ram.
Never used low-voltage devices before and wonder what way to go.

  1.. Is there a special data retention mode like on old fashion cmos? 
  If so, what will be the maxium backup voltage 
  (the devices operate normal down to 2.2V). 
  The data sheets I have are not clear about this point (if the point still exists o'cause).

  2.. What should be the better pick: NiMH or Lithium?

  3.. Also in the case of NiMH:
  Some packs list 20% of the capacity for 7 hours for optimal loading, 
  others 1mA continues charge.
  Does this matter or can both methods be used on all NiMH's?

Cheers Theo


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