Opening a spice is dead easy if you know what you're doing -- and ignore the misleading instructions on some web sites...
What you do is take out the battery and the 2 screws in the battery compartment (everyone agrees on this). You then DO NOT try to remvoe the base by 'opening it like a book'. That's how you break things.
Rather, you try to slide the base cover towards the front (0-digit) end of the machine. Place your fingers in the battery compartment, thumbs on the name strip on the front of the keyboard, and squeeze. Squeeze very hard, particularly if it's not been taken apart recently. This will free the catch at the front end. Fiddle the battery contacts through the bottom case slot, then take it off.
I seem to remember Hugh Steers shows this on his web page,
I showed him how to do it at an HPCC meeting
FWIW, Woodstocks are somewhat similar. Take out the battery, take off the 2 feet at the display end and remove the screws under them. Press on the charger pins to get them free of the case, then slide the bottom case towards the front end of the machine to free the catch. Get it free at that end, then slide it back to get the battery contacts clear and take the case off. It takes longer to explain than to do...