The cheapest way to turn on the battery when the power is off is to use a
diode. Also a small pnp + 3 resistors  current charge is required when
accu is used. I think you can't find a chip less expensive than all this
devices.
Vasile

On Wed, 17 Oct 2001, John Waters wrote:

> Hi All,
>
> My microcontroller circuit has a 62256 (32Kx8) RAM chip, which is used for
> storing some important data I want to retain even when the power is off.
> What is the normal way to retain data on RAM? Is using a battery the best
> solution? If so, how do I turn on the battery "only" when the power is off?
>
> Thanks in advance!
>
> John
>
>
>
>
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