Several factors, including the battery capacity and charging rate, affect the battery charging current. The larger the battery capacity, the higher the charge current typically is. Likewise, the higher the charging ratio, the higher the charging current and the shorter the charging time.
Amperage is the measure of electrical current, and it is critical to understand when charging a battery. A higher amperage will result in a cooler, steady power supply and shorter charge time, while a lower amperage can cause the charger to overheat.
When a battery is fully charged, the charging current drops to 0.1C. The circuit switches to constant voltage charging mode once the voltage achieves its maximum, charge cut-off voltage. The charging current of the battery steadily lowers down, and the charging rate slows down when the voltage is sustained at charge cut-off voltage.
The charging current depends directly on the capacity of the battery, all other things being equal. When you read literature about batteries, you will come across C-rate. For example: "The battery was charged at 0.5C ." It's not temperature in Celsius, and it's not capacitance in Farads.
As the battery reaches 85% of its capacity, the charging current is increased significantly. After the target voltage level is achieved, the charging current decreases and the battery gradually gets charged up to 100%.
This is why a battery charger can operate at 14-15 volts during the bulk-charge phase of the charge cycle When your battery is below 80% charged it will safely accept the higher voltage (read the spec of your battery to figure out the maximum voltage) and maximum current (Which should not be 20% of the total capacity of your battery)