Thanks for the question, Indeed you are changing the batteries correctly, The 2 screws do need to be removed and they are quite tightly fitted.
You will need a PZ1 Screwdriver or PH1 screwdriver as this is the correct size for the screws (PZ pozidrive, PH Philips) but must be a size 1 to fit the screws correctly. Wd40 should help but can take a while to penetrate.
Once you have removed the screws, the base will come off giving you access to the batteries.
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