Key Takeaway: AGM batteries require a charger with a dedicated AGM mode. Using a standard charger can damage them permanently. The CTEK MXS 5.0 and NOCO GENIUS10 are the top picks for AGM charging in Australia.
What Is an AGM Battery?
AGM (Absorbent Glass Mat) batteries are a type of sealed lead-acid battery where the electrolyte is absorbed into fibreglass mats rather than free-flooding. They're used in:
- Modern cars with stop-start systems (most cars made after 2015)
- 4WDs and dual battery setups
- Caravans and marine applications
- UPS and solar backup systems
AGM batteries are more expensive than standard flooded batteries, but they last longer, handle deep cycling better, and are maintenance-free.
Why Can't You Use a Regular Charger?
Standard chargers use a fixed voltage that's too high for AGM batteries. Overcharging an AGM battery causes the electrolyte to off-gas and dry out — permanently reducing capacity or destroying the battery.
AGM batteries need:
- Absorption voltage: 14.4–14.8V (not the 14.9–15.5V used for flooded batteries)
- Float voltage: 13.6–13.8V
- Controlled current — no fast bulk charging that floods standard chargers use
| Battery Type | Absorption Voltage | Float Voltage | Special Charger? |
|---|---|---|---|
| Flooded Lead-Acid | 14.4–14.9V | 13.2–13.8V | No |
| AGM | 14.4–14.8V | 13.6–13.8V | ✅ Yes |
| Gel | 14.0–14.4V | 13.5–13.8V | ✅ Yes |
| LiFePO4 (lithium) | 14.4–14.6V | No float | ✅ Yes |