Hog 1000 Battery

I have a Hog 1000 that, despite being around 8 years old, is still working fine but I expect that the battery will be needing replaced in the not too distant future (having heard horror stories of them leaking/corroding and damaging other circuitry within the desk)

Can anyone confirm what type of battery it uses. I'm in the UK so would be looking to get one from CPC or the likes if they have something appropriate.
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