The time a battery can supply power, also known as the runtime, can vary depending on various factors, such as the battery's capacity, the load (the electrical device it is connected to), and the efficiency of the battery.

The runtime of a battery is determined by the battery's capacity, expressed in Ampere-hour (Ah), and the power requirements of the connected device, expressed in Amperes (A). To make a rough estimate of the runtime, you simply divide the battery's capacity (Ah) by the device's power requirements (A). This provides an indication of how many hours the battery can supply power before it is fully discharged.

However, it is important to note that the actual runtime may vary due to various factors. Firstly, the actual capacity of the battery may be lower than the specified capacity due to aging, environmental conditions, and other variables. Secondly, the load may vary over time, affecting the runtime. For instance, a higher power requirement will result in a shorter runtime.

Additionally, the performance of the battery can be influenced by environmental factors such as temperature. Batteries generally have a reduced capacity at low temperatures, which can decrease the runtime.

Therefore, it is advisable to consult the specifications and recommendations of both the battery and the device manufacturer for an accurate estimate of the runtime. Based on that information, you can get a better idea of how long a battery can supply power in your specific situation.