Kenneth wrote:

<<Typically there is a watch-type battery that's easy to spot and
hopefully just as easy to pop out of its clip and replace once you
switch the computer off.>>

I'd just add to Kenneth's excellent notes:

Before you flip the old battery out, make a note of which side is facing 
up. One side is marked + and the other - .

The new battery must go in the same way round in order to preserve the 
correct polarity.

I'm not sure what would happen if you put it in the wrong way round. 
Perhaps time would be reversed, so that you could travel backwards in time 
to some bygone era.

Don Penlington

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