No issues with replacing with AGM.
That said, Costco/Interstate doesn't list a flooded-cell conventional battery for the Pilot because of the way the top battery cover fits. The cell covers on the Interstate 24 are a little bigger than those on the original Honda batteries, demanding some careful trimming of the original plastic battery top cover to fit around them. I used a pair of heavy-duty shop scissors because I have them, but any serious scissors will do the mild trimming just fine. You'll have that cover off to remove the old battery, so it's super simple to test fit and trim as needed on the new battery while both are still out of the car. Be Sure to get the 24 with the correct terminal arrangement so the cables reach.
More: I'm service life conscious for car batteries. They get annual terminal cleaning and testing, usually in the fall. That testing includes specific-gravity testing of the fluid in each cell, with battery replacement if the readings don't all come up excellent. You can get an inexpensive SPG tester at auto parts places, and I remember seeing them near the battery rack at WalMart. It's a little eye-dropper thing with colored plastic balls inside. Great when all the little balls float, with reducing capacity/condition noted when some start to sink. These testers are less than $5 last I looked. At some point I grabbed a more serious tester at NAPA for verifying a huge bank of backup batteries, one that has a calibrated float with actual SPG numbers on it. The one with the colored balls is easier to use, takes less sample fluid to fill, and is pretty foolproof to read.
The original Honda battery lasted about five years before it wouldn't reliably float all the little balls. My CTEK battery maintainers have a "rejuvenate" function that brought another year of passing the test, but by the next test it was again in need of rejuvenation. I did that, but replaced the battery anyway at that point.
-- TL;DR --
The original battery sat under my workbench for a couple more years, powering the UPS that supports the network and AV appliances cabinet plus the water heater controls. The UPS was complaining about having to charge the weakening bigger battery, so it was finally replaced/recycled at 7+ years old.
With the reduced driving the last few years thanks to the pandemic, I've been keeping all the cars on the smart CTEK maintainers between drives. Our Pilot does maybe 4k a year these days, with almost all summer duty going to one of the other toys. K drives her 4Runner all year, but it still goes on the maintainer between uses. If your use habits include the car sitting for more than a few days between uses, consider adding a smart maintainer to the car while it sits.
