The short version
If your vehicle has start-stop (the engine cuts out at red lights and restarts when you lift off the brake), you need AGM. The repeated cycling destroys flooded batteries inside two years. For everything else, flooded is fine — cheaper, the same starting performance, and the same recyclability.
Why AGM exists
AGM stands for Absorbent Glass Mat: instead of liquid electrolyte sloshing between lead plates, the electrolyte is absorbed into a fiberglass mat sandwiched between them. The construction is fully sealed, leak-proof, and — crucially — tolerates being deeply discharged and recharged thousands of times. That's the property modern vehicles need: every red light is a partial discharge, every accelerate-away is a recharge, and standard flooded plates physically shed material under that workload.
When flooded is the right call
Older vehicles without start-stop see the battery only at engine start — a one-second draw, then it sits float-charged for the rest of the drive. Flooded chemistry handles that workload indefinitely. There's no battery-life advantage to AGM in that role, and AGM costs roughly 1.5–2× as much. For a 2018 Toyota Corolla or a 2015 F-150 with the 5.0L V8 (no start-stop), flooded is the smart pick.
Edge cases worth knowing
- Cold-climate driving below −25 °C: AGM holds a higher state-of-charge in storage and recovers faster after deep discharge — useful for fly-and-drive vehicles that sit for days.
- High electrical accessory load (work trucks with inverters, RVs with house-power draws): AGM tolerates deep discharge that would kill a flooded plate set.
- Marine deep-cycle: AGM or gel — both are sealed, both tolerate trolling-motor cycling. Flooded marine starting is fine; flooded deep-cycle is a compromise.
Not sure if your vehicle has start-stop? Look at the dashboard for an A↻ icon, or check the owner's manual. Newer European cars, hybrids, and most 2018+ pickups have it; older Japanese imports and most 2015-and-earlier vehicles don't.