Hi sft456.
Gunner FVH Newick's number was 141789. Gwil mistyped it in his earlier posting on page one, and acknowledged this in post 9 above your most recent posting.
The image of the file card I attached in post 7 on page one shows the deployments of 301 Siege Battery for 1917; I don't know the original source, but given the style of handwriting it might have been from around that period (that is, during or shortly after the First World War). I got the image from the Long Long Trail website. You should read the article about the Royal Garrison Artillery, on that website (link in post

for more details about how and where the siege batteries were deployed.
In order to be included in the Electoral Register which was compiled in 1918, a serviceman would have had to complete a form which would then be sent to his local registration officer. This was organised by the military authorities, following the provisions of the 1918 Representation of the People Act which extended the franchise to all men over 21 (apart from those who were mentally unfit and Peers). The Act also allowed the vote to all men over the age of 19 who were still serving at the time of the election.
The Electoral Register did not provide the location of the absentee voters, just their unit.
The war diaries are held by the National Archives in the series WO 95. For example here is a link to the diary for 301 Siege Battery for the period March 1917 - February 1918 which you can download for free once you have registered with TNA.
https://discovery.nationalarchives.gov.uk/details/r/0ab68ec11e3f49a9980473d1a56b9014Don't expect to see your grandfather mentioned in the diary.
The medal card in post 8 on page one indicates that Fred was only awarded the British War Medal and the Victory Medal - jokingly known as Squeak and Wilfred. Because he was too young, he didn't go to France before 31 December 1915 so he wasn't eligible for the 1914-15 Star, which was referred to as Pip.