There are already a couple of battery threads here, but I may as well weigh in on the newest. I spent a couple of hours last night trying to make sense of what's out there. AGM is the latest/greatest. It's popular in motorcycles and other recreational stuff for it's non spilling and shock resistance. But what seems to be propelling it most is it's weight. It's a favorite among light aircraft owners and tricked out small-car types looking to shave lbs. In those forums seems to be the most chatter about these batteries.
I discovered that Odyessy and Deka are made in the USA. The major manufacturers are Odyessy (EnerSys Energy Products Inc made in US and England), DEKA (East Penn Manufacturing made in Lyon Station, PA) and JCI (Johnson Controls manufactured in... not sure, probably everywhere -- they don't seem to toot their horn about it). Yuasa is a well known player and there are dozens of others, mostly rebadges of the above manufacturers.
Everyone will back their favorite, and there is enough anecdotal pro and con regarding every battery on earth to fill a good slice of the world wide web. It's probably best not to even go there, except that I did find generally positive comment on DEKA along with mention of the state of the art manufacturing and single purpose focus in the DEKA plant (could just be a little Jingoism there, you never know these days, but in any case..). I checked further and there seems to be very little real complaint about these batteries. Part of the reason, of course, is that DEKA sells many more batteries rebadged than under its own name, but there was still quite a body of favorable comment on them. In particular, that the manufacturing source is predictable and of high standard, and that spec for spec they are almost half the cost of the Odyessy brand AGMs.
I found DEKA under the brand "Big Crank" here
http://www.batterymart.com/p-Big-Crank-ETX16-Battery.html"Big Crank". WTF were they thinking? If any less confidence inspiring name could have been generated among the sales staff I'm open to any suggestions ladies and gentlemen. But anyway, it seems to be a really good value. Checking a bit further I located a genuine (if only for the name printed on it, I'm sure it's still the same battery, but at least it's a 100 percent guaranty that it's original) DEKA here...
http://www.remybattery.com/Products/Performance-AGM-Power-Sports-Battery__ETX16.aspx64USD and 9USD shipping (to my michigan zip)!! Less than half overall than any Odyessy I could find.
The ETX16 is a 16amp hr battery. There's an 'L' version like in many batteries that simply refers to the location of the terminals (POS left or right) DEKA's bigger amp versions are too long for our battery space. It's hard to get a handle on the specs. The same battery is listed as 19amp hr elsewhere even though it is, obviously, nominally 16amp hr. It depends on the standards of rating it. It's an Odyessy PC680, Gruber YTX20L-BS, equivalent sizewise. Other than size, you must look closely at all the specs to decide for yourself.
The YTX20L-BS referred to in the sticky is now priced at 65USD instead of 80USD. I wondered about this and when I enhanced the photo it says it's manufactured in Vietnam. Perhaps they're no longer rebadged Odyessys? That's probably perfectly OK. Probably.
Anyway, there you go. I hope others will add their own discoveries or correct any of my errors.