Do small AGM batteries cut the mustard?

I'm trying to pick out a battery for my 13b swapped RX8. The OE battery was 350CCA and later upgraded to around 570CCA along with the 2.0kW starter to help with the hot start issues. My 6 port 13b has late closing intake and 9.4:1 rotors so it should be a little easier to turn over than the Renesis. he Odyssey PC680 and PC925 are kind of the go-to small AGM batteries but they seem to be right on the edge of daily driver functional. I won't be driving the RX8 in the winter but even spring and fall Michigan mornings are not battery friendly. This has led me search to some small AGM batteries that target the Harley bike market. They are small, cheap, claim 2X the Oddyssey CCA, and have good reviews (at least from the bike guys). Has anyone run one of these or load tested one to see if they actually pack the magic pixies they claim? For reference the PC680 is 16Ah and 170CCA weighing in at 15.4lb, PC925 is 30Ah and 330CCA at 27lb

20Ah 500CCA examples:

Renegade Wicked Start

ThrottleX X-Rated

I'm pretty sure they are all the same battery with a different label, the question is whether they really are better the competition or if it's just marketing BS.

I acquired a Prius battery that I'd like to put in the Prepared RX-7 so this thread is relevant to my interests.

I'm experimenting with a Deka ETX9 in a DD/autocross Miata this year

For many years I had an Oddyssey battery in my Alfa. It's downfall wasn't cranking- it was lack of use. The trickle down killed it deader than a door nail.

Other than that, I loved that small thing.

I can tell you that for a vehicle that is not driven regularly, an AGM will far outlast a conventional flooded lead-acid battery. I was replacing the battery in my Kawasaki almost every year, but now that I've got a generic AGM in there, it's fine whenever I feel like going for a ride. The Red Top in my RX-7 is likewise going strong after several years of infrequent use. I did recently acquire a battery tender. Now I just need to start using it.

Watching this closely as well, I'll be needing a similar battery for my RX7 in the coming weeks.

I have used the AGMs since right around they came out. Used to use the tiny ones, but settled on the ETX20 by Deka/EPM.

Good things to be said for the Deka batteries. It's worth noting that cheapo trickle chargers will kill these in no time flat. Went to a good charger and they last many years now.

I've said it a hundred times now, I'll say it again.. shorai is the best battery I've ever dealt with. I've had like 5 of em, for nearly a decade, zero failures of any kind. 5lbs, 540cca, tiny, reliable, awesome.

I had a PC680 in my LS1 Camaro, but replaced it with this one. It's much lighter, has more CCA, and has lasted over 2 years so far.

I used a Braille B14115 in my SC and it lasted for over 8 years. I just replaced it with another of the above.

I have a XSPower 680 in my 78 Z28 that weighs 15 lbs

http://www.jegs.com/i/XS-Power/703/S680/10002/-1

2 years, no issues, I leave a battery tender on it. I don't have to start the car outside in the winter time however. I will say that cold 30 degree temps it turns over easier than the 1000 CA lead battery that it had before that weighed alot more

As long as the chemistry is similar, I don't think there's going to be much difference in weight and capacity outside of the brochure. Odyssey makes good quality batteries.

On my AGM cars (almost all Odysseys) that don't get a lot of drive time, I install a battery disconnect. They'll sit happily for a year. They don't deal well with small drains (no battery does) but they'll hold a charge forever.

Keith Tanner wrote: As long as the chemistry is similar, I don't think there's going to be much difference in weight and capacity outside of the brochure. Odyssey makes good quality batteries. On my AGM cars (almost all Odysseys) that don't get a lot of drive time, I install a battery disconnect. They'll sit happily for a year. They don't deal well with small drains (no battery does) but they'll hold a charge forever.

What he said I have an Odyssey with a kill switch in the system and it absolutely amazes me how there is always enough power to crank the engine even after sitting for long periods of time.