Rider One opening

[Dave Perkins]

Hi, What type & size screw diver do I need to open a Rider One so I can replace battery?

 

[Arno]

From the picture it is a security Allan key. A hex key with dimension across the flatsand a hole drilled in the centre. Most likely 4mm or 5mm.
Since you don't need a quality forged tool check your LiDL or discounter tools house for something like

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[Dave Perkins]

Thanks in can see it's a Allen key type with pink just need a size So thank you saves buyer a set of different bits
Regards Dave

 

[Arno]

If you have a vernier caliper you can measure across the flats reliably; if not, let's see who come up with the info here.
Other TomTom's use Torx screws and when Gooleing for battery replacement on those models vendors often offer a package for tools an pry 'bar'.

Have you tried to search for battery replacement on your model?

 

[canderson]

It's so easy to pick up a small set of 1/4" hex bits. I know you're in the UK, but check this out. Dirt cheap, and solves this and MANY more problems. Surely something similar available there: