What Does the Ah Behind the Number of Volts on the Battery Mean?

AH (Ampere Hours), indicates the capacity of the battery. For example: 12v, 2AH, it means that the battery can be discharged for 1 hour with 12v voltage and 2A current.

What does the 6V, 4.5Ah on the battery mean?
Buy a dedicated battery charger. Your battery has a voltage of six volts. If the discharge capacity is calculated at one ampere per hour, it can last for 4.5 hours.

Indicates that the capacity of the battery is 4.5Ah, and the voltage is 6V.
The best charger to use is 8V4.5A charger for charging. The charging current should not exceed 5A. If the current of the charger is small, the charging time will be increased.
A device that converts chemical energy into electrical energy is called a chemical battery, generally referred to as a battery. After discharge, the internal active material can be regenerated by charging—the electrical energy is stored as chemical energy; when discharge is required, the chemical energy is converted into electrical energy again. This type of battery is called a storage battery, also called a secondary battery.
The so-called battery is an electrochemical device that stores chemical energy and releases electrical energy when necessary.