IMO, if you can find an AGM battery in the correct size and amperage range, then go for that. I was using a DEKA (US manufacturer of excellent AGM batteries) motorsports ETX-18L in my racecar. It was 10 years old and only failed due to damage from a wreck. They are reasonably priced and very good. AGM's in general seem to me to be more durable than wet batteries. Also, recently I have seen other mfg's advertising regular car-size AGM batteries.

 

^ +1

Deka is local to me, from the limited research I've done they make battery for most of the brand out there, a lot of the battery you get in store/online are just re-badged Deka with a mark up. You can get them directly from Deka for cheaper, just need to find the corresponding model number.

I have the AGM Miata battery in the rear bin, about 4 years old and it's working well for me. Pairing it with an IRP 140A alternator, my battery always read 12.3V when the car is off. If you don't let these battery drain they last a long time, and storing them in room temperature in the winter helps too (well for us with brutal winter ).

 

IMHO Optima is a lot of marketing, nothing amazing about their batteries.

I would get a good quality regular battery. Just make sure it's the right size and everything and you're good to go.

Dale

 

 

I had two of the yellow tops years ago when Costco still sold them and I had issues too. They worked OK but when they died they acted just like any other battery but for 2X+ the cost.

 

Did you have to change the alternator for an AGM to a higher voltage or did you just change it to have a better (newer) unit?

 

Braile B3121 has a crap ton of CCA and a decent amount of reserve capacity. It turns my 20b over with ease. Highly recommended!

https://www.braillebattery.com/index.php/braille/product_batteries/b3121

 

It's not required for AGM battery, but with the stock alternator I was seeing voltage as low as 13V at idle when the fans and lights are on in traffic. This could be due to the battery relocation (longer + cable) or just a tired old alternator, I did not have a PFC when I have a stock battery so I don't know if the voltage were the same then, but 13V at idle is a little out of my comfort zone, ideally I like to see 13.5V or higher with fans and lights on so I upgraded it to the IRP unit. Now I see 14V at idle, 13.8V at idle when there's load, and 13.6V when the car is super heatsoaked in traffic with fans running.

 

A Costco Interstate battery has a 36 month free replacement guarantee. Just take it back and get a new one (free). Interstate is a good brand.

 

Just had a look at the nearest Braille equivalent to Odyssey pC680,, wow, big difference in capacity for the same size,, about 1.5x the price for about 1.5x the AH and CCA. Or for the same money as a pc680 could get a smaller lighter battery with same power. Seems like good value!

 

I have the Odyssey PC1200. Like it a lot. Smaller than stock size. Will it fit? I have some room to spare with my current SMIC and my previous GReddy SMIC. Way better cranking amps, etc, as compared to the smaller PC680.
Mike

 

 

The cost is fairly prohibitive,, gets into four digits. I'm not sure why when a large motorcycle lithium does the job on paper for probably less money than a premium AGM. Maybe someone on here can explain to me the difference between a $300 motorcycle lithium vs a $2000 car lithium battery?

 

The difference is because they can charge that since most sports car enthusiasts, like us, spend at a different level of spending. The average motorcycle enthusiast can't afford a $2,000 battery. It's the same as the cost of roof on a small house in a average neighborhood is three times cheaper than the same roof, on the same size house, in a very upscale neighborhood. Same shingle, same crew, same job, different street address, much more profit!!! Greed because they can!!!
Mike

 

My 1 yet old optima yellow top 51r just took a crap on me,

Replace it with a car queast gold battery for $80 bucka, 3 year warranty

 

I have a regular 51R interstate in now and it works fine. I've had mixed luck with AGMs.

 

I've run Odyssey PC925 in my FD storage bin since I got the car in 2000. IMO it's a much better size for a street car than the PC680 that a lot of guys run but still much smaller and lighter than the stock battery.
Battery has 3 year full replacement warranty, without fail they crap out on me at 3.1 years and I have to spend another $180.
Batteries Plus stocks this battery, and a couple weeks ago when I replaced mine they had a 10% off coupon if you purchase online and pick up in the store. Made it cheaper than amazon or anywhere else I found online.

 

Ditto Tom93R1 above.

PC925 in the rear bin here. Last one lasted about 10 years while my FD was my daily. Note that I have an underdrive pulley and the "diode mod" to properly charge an AGM battery (I spoke about this in another thread, pls search).

The '925 is plenty if you don't need a ton of reserve capacity for tailgate parties or leave your lights on a lot.

 

https://www.rx7club.com/20b-forum-95.../#post11920506

 

i made a little spreadsheet of the factory info, it helps to know the stock spec before you do something else..

Miata batteries are 320cca originally and 370cca now

the Mx5 (2006+) is a 51R, 340 and 500cca

 

Speed of light,
I read the post about the diode mod and understand the concept and I want to modify my system since I just got a new AGM battery. I am uncertain, even after looking the wiring manual, which wire to cut and splice in the diode. Is the White/Green wire coming for the EGI fuse to the alternator or the Black/White wire coming for the meter fuse?
Thanks
Mike

 

 

My Costco Interstate (also a 51R) just died. It says 2011 on the sticker. I think that's pretty good, especially considering that Duralast and other auto store brands easily cost 2x as much. When did car batteries cost $150-200? It wasn't that long ago they were $50

 

They work very well and the mid sized ones can be beaten on and still turn over a high compression 3 rotor with ease, however, I've found they seem to like heat even less than a standard AGM. Put one in a tube frame GT race vehicle and it decided to internally 'splode/deform whereas the AGM that was there was a OK for many a season. I will say, however, that the placement we decided is pretty stupid from a battery longevity standpoint (too close to the cabin divider for the exhaust) but perfect from the perspective of optimal weight distro. :/