Another battery option
 

So my Advanced Autoparts U1R battery finally quit and wouldn't hold a charge after 5.5 years. The last year has been very minimal use and not always on a maintainer probably did it in... So I set out to look for a replacement. Several parts stores offer a traditional flooded type/wet cell battery, there is the Walmart $35 special lawnmower battery, and of course the AGM batteries out there as well.

Decided to go with an AGM with a Duracell sticker on it from Batteries Plus with a 2 year free replacment warranty:

https://www.batteriesplus.com/produc...-ultra/sliu1rt

Quick google search and found a 20% off code, so it ended up being about $115 out the door and they had it in stock.

Other AGM drop-in replacements I saw were of course the WestCo (1 year exchange, prorate to 4 year warranty for $128 @ Good-win right now), Deka (1 yr warranty, $134 @ amazon), Marathon (1 yr warranty, $108 @ Batterymart), and the Super Start Platinum (3 yr warranty, $160 @ O'reilly's)

Ended up with the Duracell due to price, decent warranty, and local availability.

Also, since my car doesn't get driven but once a month - if that, should I leave it on a maintainer the whole time while not in use? Or just leave it be, maybe unhook the negative terminal? Haven't had an AGM battery before and would like to maximize it's lifespan.

https://shop.advanceautoparts.com/p/...p-7/10570126-P

why not run this. Its $90 before the 20% off code and is 20lb lighter than the one you linked.

Do you run this one? How do you have the terminals connected?

I have my cars set up with a Battery Tender Jr., and leave them plugged in all the time they are not in use. I'm similar to you, in that the Miata can go a week between drives, except in Summer, so like having the battery fully charged. As a result, my battery's pretty much last forever. I like the Odyssey's, and my Elise has one from 1999 still going in it, and my NA has a newer, bigger Odyssey. The bat. tender jr. only costs around $20., and can be permanently wired in, and the lead run thru the body, so it takes a few seconds to hook up, or un-hook when taking off.

Would you have any concerns about running this in a car with an aftermarket 4-channel amp?

I used ring terminals.

Who has a stereo and tries to be as light as possible. Wouldn't recommend for that.