There are various military records for Eli on Ancestry. Each one gives information about slightly different aspects of his military service, so it is important to collect and read ALL of them.
You are lucky that Eli's WW1 service records still exist. Although a little burnt around the edges, it is possible to read most of it. It contains the most useful and interesting details.
If you want to know more about where, when and how Eli lost his life in December 1914, then his battalion's war diary is a good place to start. I have had a read of it today, and it gives some detail regarding the battle at Givenchy, where the battalion suffered a huge loss (about 50% was wiped out), including the life of your ancestor.
Let me know how you get on.