LT1driver

what does agm battery look like, how do you tell if you have one ??

MyVetteDream

You mean a GM battery? They are usually AC Delco batteries.

Or is there a battery by AGM?

GrayC5

AGM stands for Absorbed Glass Mat. This means that the battery contains glass mats that absorb the electrolyte (acid) in the battery. Some AGM batteries like the AC-Delco (now discontinued) may have "AGM" printed on one of the labels. For others you may have to go by the battery P/N and a description for that specific battery. The Optima Red Top and Yellow Top batteries people speak about here are AGM batteries.

The following from C5 Tech tips will also help you to tell if your C5's OEM battery is an AGM type: 1997 - early 2001 Battery Acid Leakage Issue.

Following are a few more links that speak to the AGM and other batteries:

Battery Tutorial

"All you ever wanted to know about AGM and Gel Cell batteries"

Here's the links to some images showing the structure of the Optima Red Top and Yellow Top batteries:

Optima Red Top Image

Optima Yellow Top Image

Finally, you should be able to find a great deal more info on AGM batteries using one of the Internet search engines, should you need it. Hope this helps.