Voltage
Voltage is the “push” or potential difference which drives current via the battery while charging. When a battery is charged, a voltage greater than the battery’s present voltage level is applied across the terminals. This increased voltage triggers the chemical reactions that allow the battery to store energy.
Current
Current is the flow of electrical charge. During charging, electricity enters the battery, supplying energy and reversing the chemical changes that occurred during discharge. The current level controls the pace at which quickly the battery charges; greater currents usually result in the faster charging, but too much current can damage the battery.
How does a battery get charged?
In general, whereas voltage supplies the energy for the charging process, current transports that power into the battery, allowing it to store electrical energy chemically. Both elements are necessary for proper battery charging.
Why is current more important?
Since a higher voltage is required to commence current flow, it has no direct connection to charging speed. A high voltage charger may have a low current output, which results in slow charging.
The battery capacity (that measured in ampere-hours, Ah) determines the total amount of electricity required for a full charge. A higher current can charge the battery faster, for as long as it stays within the safe limitations for the battery type.
Conclusion
Both voltage & current are required for battery charging.
Voltage gives the push required for current to flow.
Current is directly proportional to the charging pace and amount of energy stored in the battery.