Battery charging can be done in two ways: random charging and full-cycle charging. Random charging uses readily rechargeable, maintenance-free automotive batteries, which can be charged at any time at the AGV's backup parking station without time restrictions. Full-cycle charging requires the AGV to exit service and enter a designated charging area, and charging can only begin when the battery charge drops to a specified range. These batteries typically follow a 4-hour continuous charging followed by a 2-hour cooling cycle. Some AGVs also use a combination of these two charging methods. Charging operations can be automatic, manual, or a quick-change, pull-out type.
1. Nickel-cadmium batteries
With low internal resistance, nickel-cadmium batteries can withstand high-current discharge with minimal voltage fluctuations during discharge. Compared to other types of batteries, they are resistant to overcharging and over-discharging, and are simple and convenient to operate. The discharge voltage varies slightly depending on the discharge current, but is generally around 1.2V. The discharge termination voltage of a nickel-cadmium battery is 1.0V/cell, and its practical operating temperature range is -200°C to 600°C. It can be discharged within this range and can be repeated more than 500 times.
2. Nickel-metal hydride batteries
Nickel-metal hydride batteries have twice the energy of nickel-cadmium batteries. They can be quickly charged in one hour using a special charger, have better self-discharge characteristics than nickel-cadmium batteries, retain energy for a longer period after charging, and can be repeatedly charged and discharged more than 500 times.
3. Lithium batteries
It boasts high energy density. Compared to high-capacity nickel-cadmium batteries, its volumetric energy is 1.5 times and its energy density is twice as high. It has high voltage, with an average operating voltage of 3.6V, three times that of nickel-cadmium and nickel-metal hydride batteries. It offers a flat operating voltage and high capacity, and a wide operating temperature range of -20°C to 60°C. It has a long charge-discharge lifespan; after 500 discharge cycles, it retains at least 70% of its capacity. Lithium batteries possess characteristics such as high energy density, high voltage, and stable operation.
4. Lead-acid batteries
Lead-acid batteries are the most widely used batteries in AGVs. They use spongy lead as the negative electrode and lead dioxide as the positive electrode; these two substances are called active materials. Sulfuric acid solution is used as the electrolyte, and they work together in the battery's electrochemical reaction. AGV lead-acid batteries have advantages such as good reversibility, stable voltage characteristics, long service life, wide applicability, abundant (and renewable) raw materials, and low cost. They are mainly used in various sectors of the national economy, including transportation, mining, ports, national defense, computers, and scientific research, and are indispensable products in social production and business activities and human life.
