AGM = Absorbed Glass Mat - the electrolyte is in a somewhat gel-like base - it doesn't leak if tipped over like a wet cell, and they are generally sealed and so don't burp acid out of an overflow tube. But, they are still basically a lead/acid type of battery. The Odyssey PC680 is another such battery. These batteries have full size/capacity plates and the electrolyte suspension is generally more efficient than all but a fully topped up, proper pH level wet cell. So, you will get quite a bit of cranking amps for a fair length of time out of these. Lithium batteries can delivery alot of power quickly, but because of the typically small size of many of them - meant mainly to be able to be "hidden ins a small space" - they cannot do it for nearly so long. And, ALL batteries decline in efficiency and Ampacity as the temperatures drop. But the Lithium ones lose efficiency starting at a warmer temperature, and again, the small size they typically make them in means you've got little in reserve. If they made a Litium-ion battery the same size as the lead acid ones, they would have alot of cranking amps available. But, they are also still affected quite a bit by temperature. Even the Li batteries on the airplanes have to be insulated to maintain a consistent temperature.
The AGMs typically last longer than the unsealed lead wet cells, perhaps because they don't need someone to be mindful of topping them up periodically. But, they should also be put on a battery tender if not going to be used for extended periods of time.
