Just a thought but have you tried ringing Cambridge Mobility, from the sticker on it I'd think it was them that supplied it, they do have a web site https://www.cambridgemobility.co.uk/ phone number is 0044 1223 830 084 .

The one shown on the video appears to be a slightly different model to yours, as it has the two batteries in a single carrier and then the cover over the catch for the foldable link.
From the pictures of yours there seems to be two levers from behind where the batteries are, try pushing them up or down and maybe they will do the same as the single in the video.

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