Whether you're gearing up for your next off-grid adventure or simply maintaining your setup at home, keeping tabs on the health of your AGM (Absorbent Glass Mat) battery is essential. These deep-cycle batteries are built for durability, but like any power source, they wear down over time. The good news? You can often detect early signs of battery trouble – and in some cases, even recover a poorly performing AGM battery with the right tools and techniques.
In this guide, we’ll walk you through how to check the health of your AGM battery and help you figure out whether it’s time for a recovery effort – or a replacement.
Why AGM Battery Health Matters
AGM batteries are a popular choice in 12V power systems thanks to their maintenance-free design, vibration resistance, and relatively low self-discharge rate. But just like any battery, they’re not immune to degradation. Poor charging habits, extreme temperatures, and deep discharges can all take their toll.
Regular health checks can help you:
- Catch problems early
- Avoid unexpected power loss during a trip
- Extend the life of your battery
- Save money by restoring a recoverable battery instead of replacing it
Signs Your AGM Battery Might Be Unhealthy
Before diving into tests, it’s helpful to recognise common signs of a struggling AGM battery:
- Low voltage even after charging – This could indicate sulphation or internal resistance issues.
- Reduced run time – If your fridge or lights cut out sooner than they used to, it’s a sign of declining capacity.
- Swelling or deformation – A sign of internal damage or overcharging.
- Excessive heat during use or charge – Not normal and potentially dangerous.
- Visible corrosion or leaking – While AGM batteries are sealed, any fluid or corrosion indicates a problem.
Tools You’ll Need
To properly assess the health of your AGM battery, it’s worth having the following tools on hand:
- Multimeter or voltmeter
- Battery charger with AGM reconditioning mode (like the KickAss 22A ACDC 9 Stage Smart Charger)
- Battery load tester (optional but helpful)
- Battery monitor or shunt-based system (for real-time diagnostics over time)
Step 1: Measure Open Circuit Voltage
The first and easiest check is the open circuit voltage (OCV). This should be done after the battery has rested (no charge or discharge) for at least 12 hours.
If your battery reads under 12V, it’s likely deeply discharged. If it’s under 10.5V, it could be heavily sulphated or damaged.
Step 2: Load Testing
A load test shows how your battery performs under stress – a better indicator than voltage alone. You’ll need a dedicated load tester or a way to safely apply a consistent load (such as a 12V fridge or inverter running a known appliance).
- Fully charge the battery.
- Apply a known load for a set time (e.g. 20 amps for 5 minutes).
- Observe the voltage drop.
If voltage drops dramatically (e.g. below 10V under load), your battery may have high internal resistance or deteriorated plates.
Step 3: Charging Performance
Try charging the battery using a quality smart charger. If the charger instantly jumps to float mode or struggles to complete the cycle, the battery may be refusing charge due to sulphation.
All KickAss ACDC Smart Chargers include a Recondition Mode, which uses high-voltage pulses to break down lead sulphate crystals – often the key to recovering a neglected battery.
To attempt recovery:
- Connect the charger in Recondition Mode.
- Monitor the battery temperature – if it gets excessively hot, stop immediately.
- Run the full cycle.
- Test the voltage and load again after resting the battery.
If the voltage improves and it holds under load, you’ve potentially extended the battery’s life.
Step 4: Monitor Over Time
After recharging or recovering, monitor your battery’s behaviour for the next few cycles. A healthy AGM battery should:
- Accept and hold a charge
- Deliver consistent performance under load
- Show stable voltage after resting
Using a KickAss Battery Monitor or Mini Control Box is a great way to get real-time insight into voltage, amps, and usage trends.
When It’s Time to Replace Your AGM Battery
Unfortunately, not all batteries can be saved. You may need to retire your AGM battery if:
- It won’t charge even after reconditioning
- It won’t hold a charge for more than a few hours
- It shows physical damage (e.g. swelling, cracks)
- You’ve had it for 5+ years and performance is clearly degraded
Choosing Your Replacement
If you’re in the market for a new battery, consider upgrading to Lithium. With higher usable capacity, lighter weight, and built-in safety features, lithium batteries deliver longer life and better performance – especially for high-demand setups.
However, if you prefer to stick with AGM, make sure to choose a deep cycle model, sized correctly for your needs, and pair it with a smart charger and battery monitor for best results.
Final Thoughts
Checking the health of your AGM battery isn’t difficult – but it does require the right tools and a bit of know-how. Regular checks can help you avoid unexpected failures and save you money by catching issues early. And with features like Recondition Mode on KickAss chargers, you might even be able to breathe new life into a tired battery.
If you’re not sure whether your battery can be saved, drop into one of our retail stores or give us a ring on (07) 3123 4715. Our team of 12V experts will be happy to help you decide on the right course of action for your personal circumstances.
