This is a tough question since a definitive list is elusive. The regiments existing prior to August 1914 are well known. On the Prussian side there were 89 Feld-Artillerie Regiments (FAR), 22 Fuss-Artillierie Regiments (FuAR), and several corresponding Reserve regiments. In Bavaria, there were an additional 12 FAR and 3 FuAR. (Of course, this is not even precise, as I've seen in Cron and Jager the numbers add up +/- one or two regiments.)

It is the war-raised units that make a complete list difficult; both regiments and separate battalions. Then there are the munitions columns, which add an exponential number to the problem. And let's not forget the Matrosen Artillerie units of the Navy. Pouring through 251 Divisions shows many high numbered regiments; however, without a unit index it's time-consuming to pull together a list. I've started this task, but like all things, other priorities push it far to the bottom of my to-do list.

I was going to mention my highest number regiment collected so far; however, when I tried to open the spreadsheet that lists all of my Artillery items (including where/when purchased and how much paid), the file was corrupted and unrecoverable! Of course, this is a huge catastrophe because I have no back-up file. Guess what is now on my to-do list.