I can give you the basic idea of what you need to do.
I heard fro a guy who was NOT technical that he replaced the battery in a Zenith Superspot 286
(and it was not a problem)
computer is losing its time or date settings, or you are receiving a message:CMOS Read Error
CMOS checksum error
CMOS Battery Failure
first attempt to leave the computer on for 24 hours.
In some cases this can charge the battery and resolve your issue.
This often resolves CMOS battery related issues when a computer has
been left off for several months.
If this does not resolve your
issue follow the below steps.
Open the computer case and find the battery
on the computer MotherBoard verify that it will be accessible and that
it can be removed.
Most computers today use a coin 'cell' CMOS
battery as shown in the image below.
Just know what you are looking for.
If it were like most it would look like this:
But if not, ALL replacement batteries for the Zenith 286e on the market look like this:
Here's some example and average specs
(so yes, 3.6 lithium is OK - to answer your 2nd question)
Cylindrical cell with wires and 3 pin connector.
1.34 x 1.34 x 0.65
You should be able to solve that.
If you need more specifics go here: