Here's a really cool rich Aqua (definitely not Light Aqua!) glass battery rest insulator that looks very similar to the larger size one reported by Ed Holland but unsure of his example's measurements. This one measures 3 1/4" wide by 1 1/8" tall. Mine appears to be somewhat darker aqua than Ed's example but isn't quite as dark as the photo suggests. It was found in an old British trash dump with other objects dating from the late 1800s. There is a small glass pontil on the center base which evidently demonstrates this was hand made by blowing glass into a mold. The battery rest insulated the legs of large battery storage containers.
Based on research of British manufacturers, I believe this was made by Kilner Brothers in the Thornhill Lees factory (circa 1898-1910). Batteries were used to provide DC power for the early telegraph circuits and railroad signals. I have recovered two different pieces (that were made to be used together). This is the base. To see the top half of the insulator fitted complete with this base [id=185031591].