To maintain the correct charging current for an AGM battery, we have made one rule of thumb. The minimum charging current for an AGM battery is 10-25% of the battery capacity. As an example; for one 12V 100Ah AGM battery, we recommend charging it with a 12V battery charger with a charging current between 10A and 25A. The maximum charging current when charging AGM batteries is 30% of the battery capacity, to prevent overcharging and damage to the battery.
What happens when the charging current is too small?
Is too small a charging current harmful to an AGM battery? It is often thought that an AGM battery will fill up even with a small charging current with a long wait. But unfortunately, a battery can be damaged if the charging current is too small. Here is a technical explanation: due to gravity, the released heavy acid (during charging) will stay at the bottom of the battery. If the charging current is high enough, there will be sufficient gas formation in the battery. This creates good acid mixing in the battery, so the specific gravity of the battery acid at the top and bottom of the battery is almost the same. This significantly increases the lifespan of an AGM battery. Intercel therefore recommends that you always use a battery charger with a charging current of at least 10% of the nominal capacity of the battery.
