Lithium Battery: These are modern, lightweight, high-energy-density rechargeable batteries
12V (Voltage): This is the electrical potential of the battery. The pump motor is designed specifically to run on 12 volts DC.
2500mah (Capacity): mAh stands for milliampere-hour. It measures the energy storage capacity. A 2500mAh battery can theoretically provide 2500 milliamps (or 2.5 amps) of current for one hour, or 1.25 amps for two hours, depending on the pump's power draw.
Recharging connector 12.6V, 1A: This refers to the charger/adapter specs.
12.6V: The charger needs to put out 12.6V to fully charge a 12V lithium pack.
1A (1 Ampere): The charging speed. A 2500mAh battery charged at 1A will take approximately 2.5 to 3 hours to fully charge (2500mAh / 1000mA = 2.5 hours + charging efficiency time)