battery education sought

[Jay West]

I noticed my HP 262X terminals have a "Duracell TR133" battery in the back 
to maintain settings when powered off. The battery indicates "Mercury" on 
the side.

Are mercury batteries rechargable? I would have thought they'd use a nicad 
or something to charge up while the unit was on.

The TR133 battery also indicates "4.2V". It seems the Duracell replacement 
for this battery is Alkaline, and 4.5V. Should I use it?

Jay