Sealey TA320 Manual page 29

3. Insert the batteries into battery holder, observing the correct
polarity.
4. Put the battery cover back in place. Secure with the screws.
WARNING: To avoid electric shock, do not operate the meter until
the battery cover is in place and fastened securely.
NOTE: If your meter does not work properly, check the fuses and
batteries to make sure that they are still good and that they are
properly inserted.