Analysing The Test Data Of You AGM Deep Cycle Battery

After testing the voltage of your deep cycle battery, you can determine its state of charge by comparing the measured voltage with a state of charge table. Our State of Charge graphic shows that an AGM deep cycle battery rated at 12.30V is at a 70% state of charge. While this graphic is specific to 12V AGM deep cycle batteries, it can serve as a general guide for other battery types, although there may be slight variations in voltage rating.

Normally, a fully charged deep cycle battery should have a voltage of over 12.8V - 13V. By measuring the voltage, you can identify a few common battery problems.

If a fully charged AGM battery tests more than 20% lower than the fully charged voltage level, it may need to be replaced. This is often a sign of battery aging, damage from over/under charging, or sulfation. Using a desulfation device may sometimes improve a battery in this state, but if not, the battery may need replacement.

If a battery shows good voltage when fully charged but quickly drops the voltage to 11V or less when using power, it may have a faulty cell and require replacement. This can be caused by excessive vibration or a manufacturing defect, making repairing the faulty cells impractical.

When a deep cycle battery is completely discharged, it should read approximately 10.5V. If the voltage is below 10V, the battery may have been left in storage for too long without a charge or with a load running on it that lacks an automatic cut-off. Once the battery is below 10V, it is difficult to recharge as most battery chargers will not recognize it as a battery due to the very low voltage. However, you may be able to recharge the battery using an old bulk battery charger with no smart features, depending on how long the battery has been left at this low voltage.