Lithium Ion Batteries.

[jethro]

Yes, I have used a few of the Wally World "Neva-Start" batteries and have written about them here. Like everything in Wal-Mart, it is cheapend up enough to make you think like you are getting a good deal. The plates in the batteries are thinner because they are easier to make from recycled lead. But they work, just don't last as long in my experience. I can get 2 years out of a Neva-Start when I get 4 years out of an Interstate. The Neva-Start is about $79 when the Interstates are about $130 so it's a little more cost effective with the better battery but not that much. I use my batteries pretty hard, like 20 hours a week or more between Memorial day and Labor day.

 

[Skiffing]

Wally does not stock AGM.

They are all sealed wet cell.

 

[nsjames]

Lithium ion batteries are a fire hazard, in fact pretty much every lithium battery has that capability. Just the nature of using a highly volatile element in battery construction.

nominal lithium ion/lipo cell voltage is 3.7V.
fully charged will be 4.2
LiFE is 3.3/3.6
completely dead is somewhere about 3 depending on your cells. Anything below 3 and they're usually toast.

Those are probably LiFE chemistry. Of all the lithium technology it's the one that comes closest to lead acid voltages and is the most stable. (4s will get you 12.8 nominal, 14.4 charged) They don't tend to go up in a ball of fire like the other lithium chemistries, but it is possible.
It's also the most expensive.
There must be a charge controller in those.
probably also some temperature sensors
and some form of overcurrent protection.