Deep Cycle Batteries: AGM vs Flooded
AGM vs. Flooded Batteries: What’s the Difference, and Which One Should You Buy?
If you’ve ever had to replace a car battery, boat battery, or even a backup power battery, you’ve probably seen the terms AGM and Flooded (or “wet cell”). And if you were like most people, your first thought was something like:
“Wait… aren’t all car batteries basically the same?”
Not quite.
While they look similar, there are some big differences between AGM and Flooded lead-acid batteries. And depending on how you use your vehicle or how often it sits you might be better off with one over the other.
Let’s break it down so you can make the right choice (and maybe even save money in the long run).
What Is a Flooded Battery?
This is your classic car battery also known as a wet-cell battery.
- It has liquid electrolyte sloshing around inside.
- You can often remove the caps and check or top off water levels.
- It vents hydrogen gas when charging or discharging heavily.
- It needs to be mounted upright, and it can leak if damaged.
Flooded batteries are cheap, reliable, and widely available. They’ve been around for over a century and still work great when properly maintained.
What Is an AGM Battery?
AGM stands for Absorbent Glass Mat. Instead of free-flowing electrolyte, the acid is soaked into fiberglass mats packed tightly between the plates.
- Sealed, spill-proof design
- Charges faster and holds voltage better under load
- Resists vibration and temperature swings
- Can be mounted in any orientation
- Needs a charger with AGM-compatible voltage profiles
AGM batteries are a step up in terms of technology and price but for many people, they’re worth it.
AGM vs. Flooded: Quick Comparison
| Feature | Flooded | AGM |
| Maintenance | Needs water checks | Maintenance-free |
| Charging Speed | Slower | Faster |
| Mounting Position | Upright only | Any direction |
| Durability | Moderate | Excellent (vibration + temp) |
| Price | Lower | Higher |
| Shelf Life | 3–5 years | 5–7+ years |
| Use Case | Daily driver | Start-stop, stored vehicles, powersports |
Which One Should You Buy?
Go Flooded If…
- You’re on a tight budget
- You drive often and can recharge the battery regularly
- You don’t mind checking fluid levels once in a while
Go AGM If…
- You drive a modern car with stop/start tech or lots of electronics
- Your vehicle sits for long periods (boats, RVs, motorcycles)
- You want a battery that charges faster and lasts longer
- You live in an area with extreme heat or cold
- You just want low maintenance
Important: Use the Right Charger!
AGM batteries charge differently from flooded ones. Using the wrong charger can overcharge or undercharge your AGM and shorten its life.
Recommended tool:
NOCO Genius10 Smart Charger – It automatically detects AGM vs. Flooded, includes a repair mode, and works on everything from motorcycles to trucks.
Final Thoughts
Both flooded and AGM batteries are lead-acid at heart, but they serve different needs. If you’re after ruggedness, faster charging, and longer life, AGM is the clear winner just expect to pay a little more. For basic, everyday driving where budget matters, flooded still gets the job done.
Choose based on your needs not just the price tag, and your battery will last longer, perform better, and cause fewer headaches.