This battery was organized during the war and was a part of the Wurttemberg army which maintained a certain degree of independence from the Prussians. For that reason some of the information about the unit survived WW2 (when most of the Prussian records were destroyed) and they are held at the Landesarchiv Baden-Wurttemberg. A brief overview of the unit's service can be found on its website:
Feldartillerie-Batterie 964
Aufstellung: 24.08.1917
Auflösung: Ab 11.10.1918
Gefechtskalender
03.09.-01.12.1917 Stellungskämpfe am oberen Styr und Stochod
06.12.1917-18.02.1918 Waffenruhe/Waffenstillstand
17.04.-25.09.1918 Stellungskämpfe in den Argonnen
26.09.-05.10.1918 Durchbruchsversuch zwischen Argonnen und Maas
https://www2.landesarchiv-bw.de/ofs21/olf/struktur.php?besta...In some cases men would have been transferred about regularly - esp. if he was wounded - and so it's difficult to say if some of the other photos show the same unit. The ones where he's training would have been with a different unit most likely.