AGM (Absorbent Glass Mat) batteries offer a compelling combination of sealed maintenance-free operation, good deep cycle performance, and competitive pricing. Here is the complete guide.
>How AGM Works
The electrolyte is absorbed into a fiberglass mat sandwiched between the lead plates. The mat is >90% saturated with acid — the battery is effectively ‘dry’ in the sense that no liquid can spill.
AGM Advantages
- Sealed, spill-proof: Can be installed at any angle. No acid spills.
- No maintenance: No water top-up ever required
- Low self-discharge: 1-3% per month — stores well for seasonal use
- Low internal resistance: High discharge current capability
- Fast charging: Accepts higher charge current than flooded batteries
- No gas emission ( recombination): VRLA design recombines 99% of hydrogen gas internally
AGM Limitations
- Lower cycle life vs GEL or OPzV: 400-700 cycles @ 50% DoD
- Sensitive to overcharging: Even more sensitive than flooded — requires precise voltage control
- Temperature sensitive: Performance degrades above 40C
- Not ideal for hot climates: GEL or OPzV preferred
Better-suited AGM Applications
- UPS systems (10-30 minute backup)
- Emergency lighting
- RVs and marine (vibration-resistant)
- Solar with reliable grid backup (occasional cycling)
- Remote sites with no maintenance access
AGM Sizing for Solar
Size at 50% DoD maximum. At 50% DoD, AGM achieves ~700 cycles.