CareFusion MicroCO Operating Manual page 26

Battery life is approximately 30 hours of continuous use.
When the battery has approximately 1 hour of useful life left the alarm
will sound momentarily after the unit is first switched on and the
following message will be displayed:
When the battery has completely expired the above will be displayed
continuously and the battery must be replaced.
Locate the sliding cover situated on the rear of the unit, towards the
bottom of the device.
Place your thumb over the round thumb indent, press gently and slide
the cover to the right to remove it from the unit.
Lift the old battery out, and holding the battery terminal by the plastic
body, pull it off the old battery.
Plug the new battery into the battery terminal, taking care that the
correct polarity is observed.
Push the battery back into the battery holder, and replace the battery
cover onto the guides. Slide the battery cover to the left until it is fully
home.
Please remove the battery if the meter is likely to be unused for
some time.
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